On Thu, Jan 16, 2025 at 1:31 AM Stefano Brivio wrote:

Thanks for sticking with this. The general approach and almost the whole patch looks good to me now, but there are still a couple of issues with the options:

On Wed, 15 Jan 2025 09:18:44 +0100 Enrique Llorente wrote:

...

Both DHCPv4 and DHCPv6 has the capability to pass the hostname to clients, the DHCPv4 uses option 12 (hostname) while the DHCPv6 uses option 39 (client fqdn), for some virt deployments like kubevirt is expected to have the VirtualMachine name as the guest hostname.

This change add the following arguments: - -H --hostname NAME to configure the hostname DHCPv4 option(12) - --fqdn NAME to configure client fqdn option for both DHCPv4(81) and DHCPv6(39)

Signed-off-by: Enrique Llorente --- conf.c | 20 +++++++++-- dhcp.c | 60 ++++++++++++++++++++++++++----- dhcpv6.c | 93 ++++++++++++++++++++++++++++++++++++++++-------- passt.1 | 10 ++++++ passt.h | 5 +++ pasta.c | 17 ++++++--- test/lib/setup | 10 +++--- test/passt.mbuto | 6 ++-- test/passt/dhcp | 15 +++++++- util.c | 22 ++++++++++++ util.h | 6 ++++ 11 files changed, 226 insertions(+), 38 deletions(-)

diff --git a/conf.c b/conf.c index df2b016..0cbd625 100644 --- a/conf.c +++ b/conf.c @@ -854,7 +854,9 @@ static void usage(const char *name, FILE *f, int status) FPRINTF(f, " default: use addresses from /etc/resolv.conf\n"); FPRINTF(f, " -S, --search LIST Space-separated list, search domains\n" - " a single, empty option disables the DNS search list\n"); + " a single, empty option disables the DNS search list\n" + " -H, --hostname NAME Hostname to configure client with\n" + " --fqdn NAME FQDN to configure client with\n"); if (strstr(name, "pasta")) FPRINTF(f, " default: don't use any search list\n"); else @@ -1313,6 +1315,7 @@ void conf(struct ctx *c, int argc, char **argv) {"outbound", required_argument, NULL, 'o' }, {"dns", required_argument, NULL, 'D' }, {"search", required_argument, NULL, 'S' }, + {"hostname", required_argument, NULL, 'H' }, {"no-tcp", no_argument, &c->no_tcp, 1 }, {"no-udp", no_argument, &c->no_udp, 1 }, {"no-icmp", no_argument, &c->no_icmp, 1 }, @@ -1357,6 +1360,7 @@ void conf(struct ctx *c, int argc, char **argv) /* vhost-user backend program convention */ {"print-capabilities", no_argument, NULL, 26 }, {"socket-path", required_argument, NULL, 's' }, + {"fqdn", required_argument, NULL, 27 }, { 0 }, }; const char *logname = (c->mode == MODE_PASTA) ? "pasta" : "passt"; @@ -1379,9 +1383,9 @@ void conf(struct ctx *c, int argc, char **argv) if (c->mode == MODE_PASTA) { c->no_dhcp_dns = c->no_dhcp_dns_search = 1; fwd_default = FWD_AUTO; - optstring = "+dqfel:hF:I:p:P:m:a:n:M:g:i:o:D:S:46t:u:T:U:"; + optstring = "+dqfel:hF:I:p:P:m:a:n:M:g:i:o:D:S:H:46t:u:T:U:"; } else { - optstring = "+dqfel:hs:F:p:P:m:a:n:M:g:i:o:D:S:461t:u:"; + optstring = "+dqfel:hs:F:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:"; }

c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = FWD_UNSET; @@ -1558,6 +1562,11 @@ void conf(struct ctx *c, int argc, char **argv) case 26: vu_print_capabilities(); break; + case 27: + if (snprintf_check(c->fqdn, PASST_MAXDNAME, + "%s", optarg)) + die("Invalid FQDN: %s", optarg); + break; case 'd': c->debug = 1; c->quiet = 0; @@ -1727,6 +1736,11 @@ void conf(struct ctx *c, int argc, char **argv)

die("Cannot use DNS search domain %s", optarg); break; + case 'H': + if (snprintf_check(c->hostname, PASST_MAXDNAME, + "%s", optarg)) + die("Invalid hostname: %s", optarg); + break; case '4': v4_only = true; v6_only = false; diff --git a/dhcp.c b/dhcp.c index d8515aa..ba66f47 100644 --- a/dhcp.c +++ b/dhcp.c @@ -63,6 +63,11 @@ static struct opt opts[255];

#define OPT_MIN 60 /* RFC 951 */

+/* Total option size (excluding end option) is 576 (RFC 2131), minus + * offset of options (268), minus end option and its length (2). + */ +#define OPT_MAX 306 + /** * dhcp_init() - Initialise DHCP options */ @@ -122,7 +127,7 @@ struct msg { uint8_t sname[64]; uint8_t file[128]; uint32_t magic; - uint8_t o[308]; + uint8_t o[OPT_MAX + 2 /* End option and its length */ ]; } __attribute__((__packed__));

/** @@ -130,15 +135,28 @@ struct msg { * @m: Message to fill * @o: Option number * @offset: Current offset within options field, updated on insertion + * + * Return: false if m has space to write the option, true otherwise */ -static void fill_one(struct msg *m, int o, int *offset) +static bool fill_one(struct msg *m, int o, int *offset) { + size_t slen = opts[o].slen; + + /* If we don't have space to write the option, then just skip */ + if (*offset + 1 /* length of option */ + slen > OPT_MAX) + return true; + m->o[*offset] = o; - m->o[*offset + 1] = opts[o].slen; - memcpy(&m->o[*offset + 2], opts[o].s, opts[o].slen); + m->o[*offset + 1] = slen; + + /* Move to option */ + *offset += 2; + + memcpy(&m->o[*offset], opts[o].s, slen);

opts[o].sent = 1; - *offset += 2 + opts[o].slen; + *offset += slen; + return false; }

/** @@ -162,17 +180,20 @@ static int fill(struct msg *m) * Put it there explicitly, unless requested via option 55. */ if (opts[55].clen > 0 && !memchr(opts[55].c, 53, opts[55].clen)) - fill_one(m, 53, &offset); + if (fill_one(m, 53, &offset)) + debug("DHCP: skipping option 55");

We're skipping option 53 in this case, not 55.

...

for (i = 0; i < opts[55].clen; i++) { o = opts[55].c[i]; if (opts[o].slen != -1) - fill_one(m, o, &offset); + if (fill_one(m, o, &offset)) + debug("DHCP: skipping option %i", o); }

for (o = 0; o < 255; o++) { if (opts[o].slen != -1 && !opts[o].sent) - fill_one(m, o, &offset); + if (fill_one(m, o, &offset)) + debug("DHCP: skipping option %i", o); }

m->o[offset++] = 255; @@ -398,6 +419,29 @@ int dhcp(const struct ctx *c, const struct pool *p) if (!opts[6].slen) opts[6].slen = -1;

+ opt_len = strlen(c->hostname); + if (opt_len > 0) { + opts[12].slen = opt_len; + memcpy(opts[12].s, &c->hostname, opt_len); + }

So I tried (note the comma):

$ ./passt -d -f --hostname thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.and_get_to_253_with_this_one, -p fqdn.pcap

$ ./passt -d -f --hostname , -p fqdn.pcap

$ ./passt -d -f --hostname "" -p fqdn.pcap

the hostname and the DHCP reply are fine, but we get an empty FQDN option in the DHCPv6 reply (only).

Note that RFC 2132 (3.14) says, about option 12:

See RFC 1035 for character set restrictions.

but I'm not sure if we should validate the user input any further. I wouldn't. One might legitimately use passt to test the robustness of a DHCP client.

I understand that we are talking about two different things: - The fact that adding "," to option 12 is not ok - And DHCPv6 is broken if we don't pass --fqdn because it adds a "." field that breaks it. I will fix the DHCPv6 FQDN client option, not sure about validation input, but it's true that more or less we are going to send virtual machine names at hostnames and by kubernetes standard those should be a fqdn, so they are implicitly validated.

...

+ + opt_len = strlen(c->fqdn); + if (opt_len > 0) { + opt_len += 3 /* flags */ + + 2; /* Length byte for first label, and terminator */ + + if (sizeof(opts[81].s) < opt_len) + debug("DHCP: client FQDN option doesn't fit, skipping");

For this one, I think you actually need to maintain the check in the caller of encode_domain_name() (that is, here), because of the three bytes for the flags.

Right, I am not "skipping", I will fix that.

Otherwise, with this:

$ ./passt -d -f --fqdn thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.and_get_to_253_with_this_one, -p fqdn.pcap

this message is printed, but we end up with an option 81 with length 2, and the FQDN ends up in the padding (try and see capture).

With this:

$ ./passt -d -f --fqdn thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.and_get_to_252_with_this_one -p fqdn.pcap

length becomes 1, and the FQDN is still in the padding.

With this:

$ ./passt -d -f --fqdn thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.make_that_251_with_this_one -p fqdn.pcap

length becomes 0, end option is missing, and we have an option 4 (time server) instead.

After the fix I see just proper padding with 0 at the end, is this fine ?

With this:

$ ./passt -d -f --fqdn thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.then_its_250_with_this_one -p fqdn.pcap

things are almost fine. We get one byte of padding, which is probably not needed, but I didn't look into it.

And at this case I see proper option 81 configured with length 255 (250 + 3 /* flags */ + 2 /* first length and terminator */) So with the fix now it looks good, I am super worried that we don't have this at the tests, but we will go back to it when the proper testing framework lands.

...

+ + opts[81].s[0] = 0x4; /* flags (E) */ + opts[81].s[1] = 0xff; /* RCODE1 */ + opts[81].s[2] = 0xff; /* RCODE2 */ + + encode_domain_name((char *)opts[81].s + 3, c->fqdn); + + opts[81].slen = opt_len; + } + if (!c->no_dhcp_dns_search) opt_set_dns_search(c, sizeof(m->o));

diff --git a/dhcpv6.c b/dhcpv6.c index 0523bba..ab022d9 100644 --- a/dhcpv6.c +++ b/dhcpv6.c @@ -48,6 +48,7 @@ struct opt_hdr { # define STATUS_NOTONLINK htons_constant(4) # define OPT_DNS_SERVERS htons_constant(23) # define OPT_DNS_SEARCH htons_constant(24) +# define OPT_CLIENT_FQDN htons_constant(39) #define STR_NOTONLINK "Prefix not appropriate for link."

uint16_t l; @@ -58,6 +59,9 @@ struct opt_hdr { sizeof(struct opt_hdr)) #define OPT_VSIZE(x) (sizeof(struct opt_##x) - \ sizeof(struct opt_hdr)) +#define OPT_MAX_SIZE IPV6_MIN_MTU - (sizeof(struct ipv6hdr) + \ + sizeof(struct udphdr) + \ + sizeof(struct msg_hdr))

/** * struct opt_client_id - DHCPv6 Client Identifier option @@ -163,6 +167,18 @@ struct opt_dns_search { char list[MAXDNSRCH * NS_MAXDNAME]; } __attribute__((packed));

+/** + * struct opt_client_fqdn - Client FQDN option (RFC 4704) + * @hdr: Option header + * @flags: Flags described by RFC 4704 + * @domain_name: Client FQDN + */ +struct opt_client_fqdn { + struct opt_hdr hdr; + uint8_t flags; + char domain_name[PASST_MAXDNAME]; +} __attribute__((packed)); + /** * struct msg_hdr - DHCPv6 client/server message header * @type: DHCP message type @@ -193,6 +209,7 @@ struct msg_hdr { * @client_id: Client Identifier, variable length * @dns_servers: DNS Recursive Name Server, here just for storage size * @dns_search: Domain Search List, here just for storage size + * @client_fqdn: Client FQDN, variable length */ static struct resp_t { struct msg_hdr hdr; @@ -203,6 +220,7 @@ static struct resp_t { struct opt_client_id client_id; struct opt_dns_servers dns_servers; struct opt_dns_search dns_search; + struct opt_client_fqdn client_fqdn; } __attribute__((__packed__)) resp = { { 0 }, SERVER_ID, @@ -228,6 +246,10 @@ static struct resp_t { { { OPT_DNS_SEARCH, 0, }, { 0 }, }, + + { { OPT_CLIENT_FQDN, 0, }, + 0, { 0 }, + }, };

static const struct opt_status_code sc_not_on_link = { @@ -346,7 +368,6 @@ static size_t dhcpv6_dns_fill(const struct ctx *c, char *buf, int offset) { struct opt_dns_servers *srv = NULL; struct opt_dns_search *srch = NULL; - char *p = NULL; int i;

if (c->no_dhcp_dns) @@ -383,34 +404,75 @@ search: if (!name_len) continue;

+ name_len += 2; /* Length byte for first label, and terminator */ + if (name_len > + NS_MAXDNAME + 1 /* Length byte for first label */) { + debug("DHCP: DNS search name '%s' too long, skipping", + c->dns_search[i].n); + continue; + }

All these issues are pre-existing, but it would be nice to fix at least the DHCPv6 part of it, now that you're adding checks. With this:

I will add a check at ipv6 so they don't go beyond 255 max dns domain name len.

$ ./passt -d -f -S thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.make_this_overflow_quite_badly -p fqdn.pcap

I made the guest (dhcpcd on Alpine) hang, and with this:

$ ./passt -d -f -S thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.make_this_overflow_really_badly -p fqdn.pcap

I get a malformed DHCP packet (option 119 with length 1, then the whole string).

However, I also get a DHCPv6 option 119 with a domain list that's 256 bytes long.

I didn't test much further. The debug message never appears, but I didn't check why.

...

+ if (!srch) { srch = (struct opt_dns_search *)(buf + offset); offset += sizeof(struct opt_hdr); srch->hdr.t = OPT_DNS_SEARCH; srch->hdr.l = 0; - p = srch->list; }

- *p = '.'; - p = stpncpy(p + 1, c->dns_search[i].n, name_len); - p++; - srch->hdr.l += name_len + 2; - offset += name_len + 2; + encode_domain_name(buf + offset, c->dns_search[i].n); + + srch->hdr.l += name_len; + offset += name_len; + }

- if (srch) { - for (i = 0; i < srch->hdr.l; i++) { - if (srch->list[i] == '.') { - srch->list[i] = strcspn(srch->list + i + 1, - "."); - } - } + if (srch) srch->hdr.l = htons(srch->hdr.l); - }

return offset; }

+/** + * dhcpv6_client_fqdn_fill() - Fill in client FQDN option + * @c: Execution context + * @buf: Response message buffer where options will be appended + * @offset: Offset in message buffer for new options + * + * Return: updated length of response message buffer. + */ +static size_t dhcpv6_client_fqdn_fill(const struct pool *p, const struct ctx *c, + char *buf, int offset) + +{ + struct opt_client_fqdn const *req_opt; + struct opt_client_fqdn *o; + size_t opt_len;

dhcpv6_dns_fill() doesn't have this problem, because we have flags telling us which DNS options we should send, but here you should check that c->fqdn is actually set, otherwise we'll send an empty option when it's not specified.

...

+ opt_len = strlen(c->fqdn) + 2; /* Length byte for first label, and terminator */

This exceed 80 columns. It's also fine like that, because it's surely more readable than wrapped, but "Length of first label + terminator" makes it fit and I think it's equally clear.

I needed to refactor this so we don't have the 80 limit problem anymore.

...

+ if (opt_len > OPT_MAX_SIZE - (offset + + sizeof(struct opt_hdr) + + 1 /* flags */ )) { + debug("DHCPv6: client FQDN option doesn't fit, skipping"); + return offset; + } + + o = (struct opt_client_fqdn *)(buf + offset); + encode_domain_name(o->domain_name, c->fqdn); + req_opt = (struct opt_client_fqdn *)dhcpv6_opt(p, &(size_t){ 0 }, + OPT_CLIENT_FQDN); + if (req_opt && req_opt->flags & 0x01 /* S flag */) + o->flags = 0x02 /* O flag */; + else + o->flags = 0x00; + + opt_len++; + + o->hdr.t = OPT_CLIENT_FQDN; + o->hdr.l = htons(opt_len); + + return offset + sizeof(struct opt_hdr) + opt_len; +} + /** * dhcpv6() - Check if this is a DHCPv6 message, reply as needed * @c: Execution context @@ -544,6 +606,7 @@ int dhcpv6(struct ctx *c, const struct pool *p, n = offsetof(struct resp_t, client_id) + sizeof(struct opt_hdr) + ntohs(client_id->l); n = dhcpv6_dns_fill(c, (char *)&resp, n); + n = dhcpv6_client_fqdn_fill(p, c, (char *)&resp, n);

resp.hdr.xid = mh->xid;

diff --git a/passt.1 b/passt.1 index d9cd33e..7051fc4 100644 --- a/passt.1 +++ b/passt.1 @@ -401,6 +401,16 @@ Enable IPv6-only operation. IPv4 traffic will be ignored. By default, IPv4 operation is enabled as long as at least an IPv4 route and an interface address are configured on a given host interface.

+.TP +.BR \-H ", " \-\-hostname " " \fIname +Hostname to configure the client with. +Send \fIname\fR as DHCP option 12 (hostname). + +.TP +.BR \-\-fqdn " " \fIname +FQDN to configure the client with. +Send \fIname\fR as Client FQDN: DHCP option 81 and DHCPv6 option 39. + .SS \fBpasst\fR-only options

.TP diff --git a/passt.h b/passt.h index 0dd4efa..f3151f0 100644 --- a/passt.h +++ b/passt.h @@ -209,6 +209,8 @@ struct ip6_ctx { * @ifi4: Template interface for IPv4, -1: none, 0: IPv4 disabled * @ip: IPv4 configuration * @dns_search: DNS search list + * @hostname: Guest hostname + * @fqdn: Guest FQDN * @ifi6: Template interface for IPv6, -1: none, 0: IPv6 disabled * @ip6: IPv6 configuration * @pasta_ifn: Name of namespace interface for pasta @@ -269,6 +271,9 @@ struct ctx {

struct fqdn dns_search[MAXDNSRCH];

+ char hostname[PASST_MAXDNAME]; + char fqdn[PASST_MAXDNAME]; + int ifi6; struct ip6_ctx ip6;

diff --git a/pasta.c b/pasta.c index ff41c95..922aa10 100644 --- a/pasta.c +++ b/pasta.c @@ -169,10 +169,12 @@ void pasta_open_ns(struct ctx *c, const char *netns) * struct pasta_spawn_cmd_arg - Argument for pasta_spawn_cmd() * @exe: Executable to run * @argv: Command and arguments to run + * @ctx: Context to read config from */ struct pasta_spawn_cmd_arg { const char *exe; char *const *argv; + struct ctx *c; };

/** @@ -186,6 +188,7 @@ static int pasta_spawn_cmd(void *arg) { char hostname[HOST_NAME_MAX + 1] = HOSTNAME_PREFIX; const struct pasta_spawn_cmd_arg *a; + size_t conf_hostname_len; sigset_t set;

/* We run in a detached PID and mount namespace: mount /proc over */ @@ -195,9 +198,15 @@ static int pasta_spawn_cmd(void *arg) if (write_file("/proc/sys/net/ipv4/ping_group_range", "0 0")) warn("Cannot set ping_group_range, ICMP requests might fail");

- if (!gethostname(hostname + sizeof(HOSTNAME_PREFIX) - 1, - HOST_NAME_MAX + 1 - sizeof(HOSTNAME_PREFIX)) || - errno == ENAMETOOLONG) { + a = (const struct pasta_spawn_cmd_arg *)arg; + + conf_hostname_len = strlen(a->c->hostname); + if (conf_hostname_len > 0) { + if (sethostname(a->c->hostname, conf_hostname_len)) + warn("Unable to set configured hostname"); + } else if (!gethostname(hostname + sizeof(HOSTNAME_PREFIX) - 1, + HOST_NAME_MAX + 1 - sizeof(HOSTNAME_PREFIX)) || + errno == ENAMETOOLONG) { hostname[HOST_NAME_MAX] = '\0'; if (sethostname(hostname, strlen(hostname))) warn("Unable to set pasta-prefixed hostname"); @@ -208,7 +217,6 @@ static int pasta_spawn_cmd(void *arg) sigaddset(&set, SIGUSR1); sigwaitinfo(&set, NULL);

- a = (const struct pasta_spawn_cmd_arg *)arg; execvp(a->exe, a->argv);

die_perror("Failed to start command or shell"); @@ -230,6 +238,7 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid, struct pasta_spawn_cmd_arg arg = { .exe = argv[0], .argv = argv, + .c = c, }; char uidmap[BUFSIZ], gidmap[BUFSIZ]; char *sh_argv[] = { NULL, NULL }; diff --git a/test/lib/setup b/test/lib/setup index 580825f..ee67152 100755 --- a/test/lib/setup +++ b/test/lib/setup @@ -49,7 +49,7 @@ setup_passt() {

context_run passt "make clean" context_run passt "make valgrind" - context_run_bg passt "valgrind --max-stackframe=$((4 * 1024 * 1024)) --trace-children=yes --vgdb=no --error-exitcode=1 --suppressions=test/valgrind.supp ./passt ${__opts} -s ${STATESETUP}/passt.socket -f -t 10001 -u 10001 -P ${STATESETUP}/passt.pid" + context_run_bg passt "valgrind --max-stackframe=$((4 * 1024 * 1024)) --trace-children=yes --vgdb=no --error-exitcode=1 --suppressions=test/valgrind.supp ./passt ${__opts} -s ${STATESETUP}/passt.socket -f -t 10001 -u 10001 -H hostname1 --fqdn fqdn1.passt.test -P ${STATESETUP}/passt.pid"

# pidfile isn't created until passt is listening wait_for [ -f "${STATESETUP}/passt.pid" ] @@ -160,11 +160,11 @@ setup_passt_in_ns() { if [ ${VALGRIND} -eq 1 ]; then context_run passt "make clean" context_run passt "make valgrind" - context_run_bg passt "valgrind --max-stackframe=$((4 * 1024 * 1024)) --trace-children=yes --vgdb=no --error-exitcode=1 --suppressions=test/valgrind.supp ./passt -f ${__opts} -s ${STATESETUP}/passt.socket -t 10001,10011,10021,10031 -u 10001,10011,10021,10031 -P ${STATESETUP}/passt.pid --map-host-loopback ${__map_ns4} --map-host-loopback ${__map_ns6}" + context_run_bg passt "valgrind --max-stackframe=$((4 * 1024 * 1024)) --trace-children=yes --vgdb=no --error-exitcode=1 --suppressions=test/valgrind.supp ./passt -f ${__opts} -s ${STATESETUP}/passt.socket -H hostname1 --fqdn fqdn1.passt.test -t 10001,10011,10021,10031 -u 10001,10011,10021,10031 -P ${STATESETUP}/passt.pid --map-host-loopback ${__map_ns4} --map-host-loopback ${__map_ns6}" else context_run passt "make clean" context_run passt "make" - context_run_bg passt "./passt -f ${__opts} -s ${STATESETUP}/passt.socket -t 10001,10011,10021,10031 -u 10001,10011,10021,10031 -P ${STATESETUP}/passt.pid --map-host-loopback ${__map_ns4} --map-host-loopback ${__map_ns6}" + context_run_bg passt "./passt -f ${__opts} -s ${STATESETUP}/passt.socket -H hostname1 --fqdn fqdn1.passt.test -t 10001,10011,10021,10031 -u 10001,10011,10021,10031 -P ${STATESETUP}/passt.pid --map-host-loopback ${__map_ns4} --map-host-loopback ${__map_ns6}" fi wait_for [ -f "${STATESETUP}/passt.pid" ]

@@ -243,7 +243,7 @@ setup_two_guests() { [ ${TRACE} -eq 1 ] && __opts="${__opts} --trace" [ ${VHOST_USER} -eq 1 ] && __opts="${__opts} --vhost-user"

- context_run_bg passt_1 "./passt -s ${STATESETUP}/passt_1.socket -P ${STATESETUP}/passt_1.pid -f ${__opts} -t 10001 -u 10001" + context_run_bg passt_1 "./passt -s ${STATESETUP}/passt_1.socket -P ${STATESETUP}/passt_1.pid -f ${__opts} --fqdn fqdn1.passt.test -H hostname1 -t 10001 -u 10001" wait_for [ -f "${STATESETUP}/passt_1.pid" ]

__opts= @@ -252,7 +252,7 @@ setup_two_guests() { [ ${TRACE} -eq 1 ] && __opts="${__opts} --trace" [ ${VHOST_USER} -eq 1 ] && __opts="${__opts} --vhost-user"

- context_run_bg passt_2 "./passt -s ${STATESETUP}/passt_2.socket -P ${STATESETUP}/passt_2.pid -f ${__opts} -t 10004 -u 10004" + context_run_bg passt_2 "./passt -s ${STATESETUP}/passt_2.socket -P ${STATESETUP}/passt_2.pid -f ${__opts} --hostname hostname2 --fqdn fqdn2 -t 10004 -u 10004" wait_for [ -f "${STATESETUP}/passt_2.pid" ]

__vmem="$((${MEM_KIB} / 1024 / 4))" diff --git a/test/passt.mbuto b/test/passt.mbuto index 138d365..1e07693 100755 --- a/test/passt.mbuto +++ b/test/passt.mbuto @@ -13,7 +13,7 @@ PROGS="${PROGS:-ash,dash,bash ip mount ls insmod mkdir ln cat chmod lsmod modprobe find grep mknod mv rm umount jq iperf3 dhclient hostname sed tr chown sipcalc cut socat dd strace ping tail killall sleep sysctl - nproc tcp_rr tcp_crr udp_rr which tee seq bc sshd ssh-keygen cmp}" + nproc tcp_rr tcp_crr udp_rr which tee seq bc sshd ssh-keygen cmp env}"

# OpenSSH 9.8 introduced split binaries, with sshd being the daemon, and # sshd-session the per-session program. We need the latter as well, and the path @@ -41,6 +41,7 @@ FIXUP="${FIXUP}"' #!/bin/sh LOG=/var/log/dhclient-script.log echo \${reason} \${interface} >> \$LOG +env >> \$LOG set >> \$LOG

[ -n "\${new_interface_mtu}" ] && ip link set dev \${interface} mtu \${new_interface_mtu} @@ -54,7 +55,8 @@ set >> \$LOG [ -n "\${new_ip6_address}" ] && ip addr add \${new_ip6_address}/\${new_ip6_prefixlen} dev \${interface} [ -n "\${new_dhcp6_name_servers}" ] && for d in \${new_dhcp6_name_servers}; do echo "nameserver \${d}%\${interface}" >> /etc/resolv.conf; done [ -n "\${new_dhcp6_domain_search}" ] && (printf "search"; for d in \${new_dhcp6_domain_search}; do printf " %s" "\${d}"; done; printf "\n") >> /etc/resolv.conf -[ -n "\${new_host_name}" ] && hostname "\${new_host_name}" +[ -n "\${new_host_name}" ] && echo "\${new_host_name}" > /tmp/new_host_name +[ -n "\${new_fqdn_fqdn}" ] && echo "\${new_fqdn_fqdn}" > /tmp/new_fqdn_fqdn exit 0 EOF chmod 755 /sbin/dhclient-script diff --git a/test/passt/dhcp b/test/passt/dhcp index 9925ab9..145f1ba 100644 --- a/test/passt/dhcp +++ b/test/passt/dhcp @@ -11,7 +11,7 @@ # Copyright (c) 2021 Red Hat GmbH # Author: Stefano Brivio

-gtools ip jq dhclient sed tr +gtools ip jq dhclient sed tr hostname htools ip jq sed tr head

test Interface name @@ -47,7 +47,16 @@ gout SEARCH sed 's/\. / /g' /etc/resolv.conf | sed 's/\.$//g' | sed -n 's/^searc hout HOST_SEARCH sed 's/\. / /g' /etc/resolv.conf | sed 's/\.$//g' | sed -n 's/^search \(.*\)/\1/p' | tr ' \n' ',' | sed 's/,$//;s/$/\n/' check [ "__SEARCH__" = "__HOST_SEARCH__" ]

+test DHCP: Hostname +gout NEW_HOST_NAME cat /tmp/new_host_name +check [ "__NEW_HOST_NAME__" = "hostname1" ] + +test DHCP: Client FQDN +gout NEW_FQDN_FQDN cat /tmp/new_fqdn_fqdn +check [ "__NEW_FQDN_FQDN__" = "fqdn1.passt.test" ] + test DHCPv6: address +guest rm /tmp/new_fqdn_fqdn guest /sbin/dhclient -6 __IFNAME__ # Wait for DAD to complete guest while ip -j -6 addr show tentative | jq -e '.[].addr_info'; do sleep 0.1; done @@ -70,3 +79,7 @@ test DHCPv6: search list gout SEARCH6 sed 's/\. / /g' /etc/resolv.conf | sed 's/\.$//g' | sed -n 's/^search \(.*\)/\1/p' | tr ' \n' ',' | sed 's/,$//;s/$/\n/' hout HOST_SEARCH6 sed 's/\. / /g' /etc/resolv.conf | sed 's/\.$//g' | sed -n 's/^search \(.*\)/\1/p' | tr ' \n' ',' | sed 's/,$//;s/$/\n/' check [ "__SEARCH6__" = "__HOST_SEARCH6__" ] + +test DHCPv6: Hostname +gout NEW_FQDN_FQDN cat /tmp/new_fqdn_fqdn +check [ "__NEW_FQDN_FQDN__" = "fqdn1.passt.test" ] diff --git a/util.c b/util.c index 11973c4..575a879 100644 --- a/util.c +++ b/util.c @@ -837,3 +837,25 @@ void raw_random(void *buf, size_t buflen) if (random_read < buflen) die("Unexpected EOF on random data source"); } +/** + * encode_domain_name() - Encode domain name according to RFC 1035, section 3.1 + * @buf: Buffer to fill in with encoded domain name + * @domain_name: Input domain name string with terminator + * + * The buffer's 'buf' size has to be >= strlen(domain_name) + 2 + */ +void encode_domain_name(char *buf, const char *domain_name) +{ + size_t i; + char *p; + + buf[0] = strcspn(domain_name, "."); + p = buf + 1; + for (i = 0; domain_name[i]; i++) { + if (domain_name[i] == '.') + p[i] = strcspn(domain_name + i + 1, "."); + else + p[i] = domain_name[i]; + } + p[i] = 0L; +} diff --git a/util.h b/util.h index 3fa1d12..0744276 100644 --- a/util.h +++ b/util.h @@ -40,6 +40,9 @@ #ifndef IP_MAX_MTU #define IP_MAX_MTU USHRT_MAX #endif +#ifndef IPV6_MIN_MTU +#define IPV6_MIN_MTU 1280 +#endif

#ifndef MIN #define MIN(x, y) (((x) < (y)) ? (x) : (y)) @@ -346,4 +349,7 @@ static inline int wrap_accept4(int sockfd, struct sockaddr *addr, #define accept4(s, addr, addrlen, flags) \ wrap_accept4((s), (addr), (addrlen), (flags))

+#define PASST_MAXDNAME 254 /* 253 (RFC 1035) + 1 (the terminator) */ +void encode_domain_name(char *buf, const char *domain_name); + #endif /* UTIL_H */

The rest looks good to me.

Sending new patch with the fixes.

-- Stefano

-- Quique Llorente CNV networking Senior Software Engineer Red Hat EMEA ellorent@redhat.com @RedHat Red Hat Red Hat

On Wed, Jan 22, 2025 at 1:29 PM Stefano Brivio wrote:

On Wed, 22 Jan 2025 13:09:07 +0100 Enrique Llorente Pastora wrote:

...

On Thu, Jan 16, 2025 at 1:31 AM Stefano Brivio wrote:

...

Thanks for sticking with this. The general approach and almost the whole patch looks good to me now, but there are still a couple of issues with the options:

On Wed, 15 Jan 2025 09:18:44 +0100 Enrique Llorente wrote:

...

Both DHCPv4 and DHCPv6 has the capability to pass the hostname to clients, the DHCPv4 uses option 12 (hostname) while the DHCPv6 uses option 39 (client fqdn), for some virt deployments like kubevirt is expected to have the VirtualMachine name as the guest hostname.

This change add the following arguments: - -H --hostname NAME to configure the hostname DHCPv4 option(12) - --fqdn NAME to configure client fqdn option for both DHCPv4(81) and DHCPv6(39)

Signed-off-by: Enrique Llorente --- conf.c | 20 +++++++++-- dhcp.c | 60 ++++++++++++++++++++++++++----- dhcpv6.c | 93 ++++++++++++++++++++++++++++++++++++++++-------- passt.1 | 10 ++++++ passt.h | 5 +++ pasta.c | 17 ++++++--- test/lib/setup | 10 +++--- test/passt.mbuto | 6 ++-- test/passt/dhcp | 15 +++++++- util.c | 22 ++++++++++++ util.h | 6 ++++ 11 files changed, 226 insertions(+), 38 deletions(-)

diff --git a/conf.c b/conf.c index df2b016..0cbd625 100644 --- a/conf.c +++ b/conf.c @@ -854,7 +854,9 @@ static void usage(const char *name, FILE *f, int status) FPRINTF(f, " default: use addresses from /etc/resolv.conf\n"); FPRINTF(f, " -S, --search LIST Space-separated list, search domains\n" - " a single, empty option disables the DNS search list\n"); + " a single, empty option disables the DNS search list\n" + " -H, --hostname NAME Hostname to configure client with\n" + " --fqdn NAME FQDN to configure client with\n"); if (strstr(name, "pasta")) FPRINTF(f, " default: don't use any search list\n"); else @@ -1313,6 +1315,7 @@ void conf(struct ctx *c, int argc, char **argv) {"outbound", required_argument, NULL, 'o' }, {"dns", required_argument, NULL, 'D' }, {"search", required_argument, NULL, 'S' }, + {"hostname", required_argument, NULL, 'H' }, {"no-tcp", no_argument, &c->no_tcp, 1 }, {"no-udp", no_argument, &c->no_udp, 1 }, {"no-icmp", no_argument, &c->no_icmp, 1 }, @@ -1357,6 +1360,7 @@ void conf(struct ctx *c, int argc, char **argv) /* vhost-user backend program convention */ {"print-capabilities", no_argument, NULL, 26 }, {"socket-path", required_argument, NULL, 's' }, + {"fqdn", required_argument, NULL, 27 }, { 0 }, }; const char *logname = (c->mode == MODE_PASTA) ? "pasta" : "passt"; @@ -1379,9 +1383,9 @@ void conf(struct ctx *c, int argc, char **argv) if (c->mode == MODE_PASTA) { c->no_dhcp_dns = c->no_dhcp_dns_search = 1; fwd_default = FWD_AUTO; - optstring = "+dqfel:hF:I:p:P:m:a:n:M:g:i:o:D:S:46t:u:T:U:"; + optstring = "+dqfel:hF:I:p:P:m:a:n:M:g:i:o:D:S:H:46t:u:T:U:"; } else { - optstring = "+dqfel:hs:F:p:P:m:a:n:M:g:i:o:D:S:461t:u:"; + optstring = "+dqfel:hs:F:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:"; }

c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = FWD_UNSET; @@ -1558,6 +1562,11 @@ void conf(struct ctx *c, int argc, char **argv) case 26: vu_print_capabilities(); break; + case 27: + if (snprintf_check(c->fqdn, PASST_MAXDNAME, + "%s", optarg)) + die("Invalid FQDN: %s", optarg); + break; case 'd': c->debug = 1; c->quiet = 0; @@ -1727,6 +1736,11 @@ void conf(struct ctx *c, int argc, char **argv)

die("Cannot use DNS search domain %s", optarg); break; + case 'H': + if (snprintf_check(c->hostname, PASST_MAXDNAME, + "%s", optarg)) + die("Invalid hostname: %s", optarg); + break; case '4': v4_only = true; v6_only = false; diff --git a/dhcp.c b/dhcp.c index d8515aa..ba66f47 100644 --- a/dhcp.c +++ b/dhcp.c @@ -63,6 +63,11 @@ static struct opt opts[255];

#define OPT_MIN 60 /* RFC 951 */

+/* Total option size (excluding end option) is 576 (RFC 2131), minus + * offset of options (268), minus end option and its length (2). + */ +#define OPT_MAX 306 + /** * dhcp_init() - Initialise DHCP options */ @@ -122,7 +127,7 @@ struct msg { uint8_t sname[64]; uint8_t file[128]; uint32_t magic; - uint8_t o[308]; + uint8_t o[OPT_MAX + 2 /* End option and its length */ ]; } __attribute__((__packed__));

/** @@ -130,15 +135,28 @@ struct msg { * @m: Message to fill * @o: Option number * @offset: Current offset within options field, updated on insertion + * + * Return: false if m has space to write the option, true otherwise */ -static void fill_one(struct msg *m, int o, int *offset) +static bool fill_one(struct msg *m, int o, int *offset) { + size_t slen = opts[o].slen; + + /* If we don't have space to write the option, then just skip */ + if (*offset + 1 /* length of option */ + slen > OPT_MAX) + return true; + m->o[*offset] = o; - m->o[*offset + 1] = opts[o].slen; - memcpy(&m->o[*offset + 2], opts[o].s, opts[o].slen); + m->o[*offset + 1] = slen; + + /* Move to option */ + *offset += 2; + + memcpy(&m->o[*offset], opts[o].s, slen);

opts[o].sent = 1; - *offset += 2 + opts[o].slen; + *offset += slen; + return false; }

/** @@ -162,17 +180,20 @@ static int fill(struct msg *m) * Put it there explicitly, unless requested via option 55. */ if (opts[55].clen > 0 && !memchr(opts[55].c, 53, opts[55].clen)) - fill_one(m, 53, &offset); + if (fill_one(m, 53, &offset)) + debug("DHCP: skipping option 55");

We're skipping option 53 in this case, not 55.

...

for (i = 0; i < opts[55].clen; i++) { o = opts[55].c[i]; if (opts[o].slen != -1) - fill_one(m, o, &offset); + if (fill_one(m, o, &offset)) + debug("DHCP: skipping option %i", o); }

for (o = 0; o < 255; o++) { if (opts[o].slen != -1 && !opts[o].sent) - fill_one(m, o, &offset); + if (fill_one(m, o, &offset)) + debug("DHCP: skipping option %i", o); }

m->o[offset++] = 255; @@ -398,6 +419,29 @@ int dhcp(const struct ctx *c, const struct pool *p) if (!opts[6].slen) opts[6].slen = -1;

+ opt_len = strlen(c->hostname); + if (opt_len > 0) { + opts[12].slen = opt_len; + memcpy(opts[12].s, &c->hostname, opt_len); + }

So I tried (note the comma):

$ ./passt -d -f --hostname thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.and_get_to_253_with_this_one, -p fqdn.pcap

$ ./passt -d -f --hostname , -p fqdn.pcap

$ ./passt -d -f --hostname "" -p fqdn.pcap

the hostname and the DHCP reply are fine, but we get an empty FQDN option in the DHCPv6 reply (only).

Note that RFC 2132 (3.14) says, about option 12:

See RFC 1035 for character set restrictions.

but I'm not sure if we should validate the user input any further. I wouldn't. One might legitimately use passt to test the robustness of a DHCP client.

I understand that we are talking about two different things: - The fact that adding "," to option 12 is not ok

No, I think it's actually fine, I just wanted to make you aware of that.

...

- And DHCPv6 is broken if we don't pass --fqdn because it adds a "." field that breaks it.

Right, yes.

...

I will fix the DHCPv6 FQDN client option, not sure about validation input, but it's true that more or less we are going to send virtual machine names at hostnames and by kubernetes standard those should be a fqdn, so they are implicitly validated.

Well, this is completely independent of what Kubernetes might do with it one day. But still, I would *not* validate it because passt is also quite useful (and used) to test this kind of stuff.

...

...

...

+ + opt_len = strlen(c->fqdn); + if (opt_len > 0) { + opt_len += 3 /* flags */ + + 2; /* Length byte for first label, and terminator */ + + if (sizeof(opts[81].s) < opt_len) + debug("DHCP: client FQDN option doesn't fit, skipping");

For this one, I think you actually need to maintain the check in the caller of encode_domain_name() (that is, here), because of the three bytes for the flags.

Right, I am not "skipping", I will fix that.

...

Otherwise, with this:

$ ./passt -d -f --fqdn thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.and_get_to_253_with_this_one, -p fqdn.pcap

this message is printed, but we end up with an option 81 with length 2, and the FQDN ends up in the padding (try and see capture).

With this:

$ ./passt -d -f --fqdn thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.and_get_to_252_with_this_one -p fqdn.pcap

length becomes 1, and the FQDN is still in the padding.

With this:

$ ./passt -d -f --fqdn thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.make_that_251_with_this_one -p fqdn.pcap

length becomes 0, end option is missing, and we have an option 4 (time server) instead.

After the fix I see just proper padding with 0 at the end, is this fine ?

Probably. We just shouldn't have unnecessary padding.

By the way, this change should depend on another change *not* reusing the original message as buffer for the reply, as discussed.

Totally forgot about that, should I make a patchset or different changes ?

...

...

With this:

$ ./passt -d -f --fqdn thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.then_its_250_with_this_one -p fqdn.pcap

things are almost fine. We get one byte of padding, which is probably not needed, but I didn't look into it.

And at this case I see proper option 81 configured with length 255 (250 + 3 /* flags */ + 2 /* first length and terminator */)

So with the fix now it looks good, I am super worried that we don't have this at the tests, but we will go back to it when the proper testing framework lands.

I'm not, in the sense that this isn't really security relevant *unless we leak host memory into the guest*. The rest is a functional issue, and it's not easy to break this "by mistake".

Sure, ideally we should have tests for those, but... they don't break by themselves. This code is pretty much isolated and stand-alone.

Fair enough.

-- Stefano

-- Quique Llorente CNV networking Senior Software Engineer Red Hat EMEA ellorent@redhat.com @RedHat Red Hat Red Hat