On Sun, Feb 08, 2026 at 07:37:27PM -0500, Jon Maloy wrote:
Extend the -a/--address option to accept addresses in CIDR notation (e.g., 192.168.1.1/24 or 2001:db8::1/64) as an alternative to using separate -a and -n options.
We add a new inany_prefix_pton() helper function that: - Parses address strings with a compulsory /prefix_len suffix - Validates prefix length based on address family (0-32 for IPv4, 0-128 for IPv6), including handling of IPv4-to-IPv6 mapping case.
For IPv4, the prefix length is stored in ip4.prefix_len when provided. Mixing -n and CIDR notation results in an error to catch likely user mistakes.
Also fix a bug in conf_ip4_prefix() that was incorrectly using the global 'optarg' instead of its 'arg' parameter.
Signed-off-by: Jon Maloy
I have some comments below, but none of them are showstoppers, so:
Reviewed-by: David Gibson
--- v3: Fixes after feedback from Laurent, David and Stefano Notably, updated man page for the -a option
v4: Fixes based on feedback from David G: - Handling prefix length adjustment when IPv4-to-IPv6 mapping - Removed redundant !IN6_IS_ADDR_V4MAPPED(&addr.a6) test - Simplified tests of acceptable address types - Merged documentation and code commits - Some documentation text clarifications
v5: - Moved address/prefix parsing into a refactored inany_prefix_pton() function. - inany_prefix_pton() now only caluclates IPv6 style prefix lengths - Stricter distinction between error causes. - Some refactoring of the 'case a:' branch in conf() - Some small fixes in passt.1
v6: - Refactored inany_prefix_pton() and conf()::'case -a' code after input from David Gibson.
v7: - More refactoring after input from David Gibson. - I kept the return values 1 and 0. This is consistent with the return values of inet_pton() and inany_pton().
Ah, good point, my mistake.
v8: - Changed condition for updating ipv4 prefix length
v9: - Made char *src and char *pstr in inany_prefix_pton() const - Updated logics in conf.c:: case 'a' and case 'n' to be clearer (I think) --- conf.c | 72 +++++++++++++++++++++++++++++++++++++-------------------- inany.c | 51 ++++++++++++++++++++++++++++++++++++++++ inany.h | 15 ++++++++++++ ip.c | 21 +++++++++++++++++ ip.h | 2 ++ passt.1 | 17 ++++++++++---- 6 files changed, 148 insertions(+), 30 deletions(-)
diff --git a/conf.c b/conf.c index 2942c8c..46cfb6e 100644 --- a/conf.c +++ b/conf.c @@ -682,7 +682,7 @@ static int conf_ip4_prefix(const char *arg) return -1; } else { errno = 0; - len = strtoul(optarg, NULL, 0); + len = strtoul(arg, NULL, 0); if (len > 32 || errno) return -1; } @@ -896,7 +896,7 @@ static void usage(const char *name, FILE *f, int status) " a zero value disables assignment\n" " default: 65520: maximum 802.3 MTU minus 802.3 header\n" " length, rounded to 32 bits (IPv4 words)\n" - " -a, --address ADDR Assign IPv4 or IPv6 address ADDR\n" + " -a, --address ADDR Assign IPv4 or IPv6 address ADDR[/PREFIXLEN]\n" " can be specified zero to two times (for IPv4 and IPv6)\n" " default: use addresses from interface with default route\n" " -n, --netmask MASK Assign IPv4 MASK, dot-decimal or bits\n" @@ -1505,6 +1505,8 @@ void conf(struct ctx *c, int argc, char **argv) unsigned long max_mtu = IP_MAX_MTU; struct fqdn *dnss = c->dns_search; unsigned int ifi4 = 0, ifi6 = 0; + bool prefix_from_cidr = false; + uint8_t prefix_from_opt = 0;
I see why, but having two variables with very similarly formatted names, but different types and semantics is potentially confusing. Using '0' as a nil value for the prefix length also makes me nervous, since 0 length prefixes are in general valid, even if they're not useful for the -a option.
const char *logfile = NULL; size_t logsize = 0; char *runas = NULL; @@ -1808,36 +1810,56 @@ void conf(struct ctx *c, int argc, char **argv) c->mtu = mtu; break; } - case 'a': - if (inet_pton(AF_INET6, optarg, &c->ip6.addr) && - !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr) && - !IN6_IS_ADDR_LOOPBACK(&c->ip6.addr) && - !IN6_IS_ADDR_V4MAPPED(&c->ip6.addr) && - !IN6_IS_ADDR_V4COMPAT(&c->ip6.addr) && - !IN6_IS_ADDR_MULTICAST(&c->ip6.addr)) { - if (c->mode == MODE_PASTA) - c->ip6.no_copy_addrs = true; - break; - } + case 'a': { + union inany_addr addr; + uint8_t prefix_len; + + prefix_from_cidr = + inany_prefix_pton(optarg, &addr, &prefix_len); + + if (prefix_from_cidr && prefix_from_opt) + die("Can't mix CIDR with -n"); + + if (!prefix_from_cidr && !inany_pton(optarg, &addr)) + die("Invalid address: %s", optarg); + + if (prefix_from_opt && inany_v4(&addr)) + prefix_len = prefix_from_opt; + else if (!prefix_from_cidr) + prefix_len = inany_default_prefix_len(&addr); + + if (inany_is_unspecified(&addr) || + inany_is_multicast(&addr) || + inany_is_loopback(&addr) || + IN6_IS_ADDR_V4COMPAT(&addr.a6)) + die("Invalid address: %s", optarg);
- if (inet_pton(AF_INET, optarg, &c->ip4.addr) && - !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr) && - !IN4_IS_ADDR_BROADCAST(&c->ip4.addr) && - !IN4_IS_ADDR_LOOPBACK(&c->ip4.addr) && - !IN4_IS_ADDR_MULTICAST(&c->ip4.addr)) { + if (inany_v4(&addr)) { + c->ip4.addr = *inany_v4(&addr); + c->ip4.prefix_len = prefix_len - 96; if (c->mode == MODE_PASTA) c->ip4.no_copy_addrs = true; - break; + } else { + c->ip6.addr = addr.a6; + if (c->mode == MODE_PASTA) + c->ip6.no_copy_addrs = true; } - - die("Invalid address: %s", optarg); break; - case 'n': - c->ip4.prefix_len = conf_ip4_prefix(optarg); - if (c->ip4.prefix_len < 0) - die("Invalid netmask: %s", optarg); + } + case 'n': { + int plen; + + if (prefix_from_cidr) + die("Can't use both -n and CIDR prefix length");
+ plen = conf_ip4_prefix(optarg); + if (plen < 0) + die("Invalid prefix length: %s", optarg); + + prefix_from_opt = plen + 96;
Since it's only used for IPv4 adddresses, prefix_from_opt could encode in IPv4-style (0..32, rather than 0..128). I don't have a strong preference, though.
+ c->ip4.prefix_len = plen; break; + } case 'M': parse_mac(c->our_tap_mac, optarg); break; diff --git a/inany.c b/inany.c index 7680439..df6a126 100644 --- a/inany.c +++ b/inany.c @@ -11,6 +11,7 @@ #include
#include #include +#include #include "util.h" #include "ip.h" @@ -57,3 +58,53 @@ int inany_pton(const char *src, union inany_addr *dst)
return 0; } + +/** + * inany_prefix_pton() - Parse an IPv[46] address with prefix length + * @src: IPv[46] address and prefix length string in CIDR format + * @dst: Output buffer, filled with parsed address + * @prefix_len: Prefix length, to be filled in IPv6 format + * + * Return: on success, 1, if no parseable address or prefix is found, 0 + */ +int inany_prefix_pton(const char *src, union inany_addr *dst, + uint8_t *prefix_len) +{ + char astr[INANY_ADDRSTRLEN] = {0,};
I don't believe this needs an initializer.
+ size_t alen = strcspn(src, "/"); + const char *pstr = &src[alen + 1]; + unsigned long plen; + char *end; + + if (alen >= INANY_ADDRSTRLEN) + return 0; + + if (src[alen] != '/') + return 0; + + strncpy(astr, src, alen); + + /* Read prefix length */ + errno = 0; + plen = strtoul(pstr, &end, 10); + if (errno || *end || plen > 128) + return 0; + + *prefix_len = plen;
It would be slightly cleaner not to clobber any of the output parameters on failure, but it's not a big deal.
+ + /* Read address */ + if (inet_pton(AF_INET6, astr, dst)) { + if (inany_v4(dst) && *prefix_len < 96) + return 0; + return 1; + } + + if (inany_pton(astr, dst)) { + if (*prefix_len > 32) + return 0; + *prefix_len += 96; + return 1; + } + + return 0; +} diff --git a/inany.h b/inany.h index 61b36fb..c7d6027 100644 --- a/inany.h +++ b/inany.h @@ -96,6 +96,19 @@ static inline struct in_addr *inany_v4(const union inany_addr *addr) return (struct in_addr *)&addr->v4mapped.a4; }
+/** inany_default_prefix_len() - Get default prefix length for address + * @addr: IPv4 or iPv6 address + * + * Return: Class-based prefix length for IPv4 (in IPv6 format: 104-128), + * or 64 for IPv6 + */ +static inline int inany_default_prefix_len(const union inany_addr *addr) +{ + const struct in_addr *v4 = inany_v4(addr); + + return v4 ? ip4_class_prefix_len(v4) + 96 : 64; +} + /** inany_equals - Compare two IPv[46] addresses * @a, @b: IPv[46] addresses * @@ -295,5 +308,7 @@ static inline void inany_siphash_feed(struct siphash_state *state,
const char *inany_ntop(const union inany_addr *src, char *dst, socklen_t size); int inany_pton(const char *src, union inany_addr *dst); +int inany_prefix_pton(const char *src, union inany_addr *dst, + uint8_t *prefix_len);
#endif /* INANY_H */ diff --git a/ip.c b/ip.c index 9a7f4c5..40dc24e 100644 --- a/ip.c +++ b/ip.c @@ -13,6 +13,8 @@ */
#include
+#include + #include "util.h" #include "ip.h" @@ -67,3 +69,22 @@ found: *proto = nh; return true; } + +/** + * ip4_class_prefix_len() - Get class based prefix length for IPv4 address + * @addr: IPv4 address + * + * Return: prefix length based on address class, or 32 for other + */ +int ip4_class_prefix_len(const struct in_addr *addr) +{ + in_addr_t a = ntohl(addr->s_addr); + + if (IN_CLASSA(a)) + return 32 - IN_CLASSA_NSHIFT; + if (IN_CLASSB(a)) + return 32 - IN_CLASSB_NSHIFT; + if (IN_CLASSC(a)) + return 32 - IN_CLASSC_NSHIFT; + return 32; +} diff --git a/ip.h b/ip.h index 5830b92..bd28640 100644 --- a/ip.h +++ b/ip.h @@ -135,4 +135,6 @@ static const struct in_addr in4addr_broadcast = { 0xffffffff }; #define IPV6_MIN_MTU 1280 #endif
+int ip4_class_prefix_len(const struct in_addr *addr); + #endif /* IP_H */ diff --git a/passt.1 b/passt.1 index db0d662..2c3eae9 100644 --- a/passt.1 +++ b/passt.1 @@ -156,10 +156,14 @@ By default, the advertised MTU is 65520 bytes, that is, the maximum 802.3 MTU minus the length of a 802.3 header, rounded to 32 bits (IPv4 words).
.TP -.BR \-a ", " \-\-address " " \fIaddr +.BR \-a ", " \-\-address " " \fIaddr\fR[/\fIprefix_len\fR] Assign IPv4 \fIaddr\fR via DHCP (\fByiaddr\fR), or \fIaddr\fR via DHCPv6 (option 5) and an \fIaddr\fR-based prefix via NDP Router Advertisement (option type 3) for an IPv6 \fIaddr\fR. +An optional /\fIprefix_len\fR (0-32 for IPv4, 0-128 for IPv6) can be +appended in CIDR notation (e.g. 192.0.2.1/24). This is an alternative to +using the \fB-n\fR, \fB--netmask\fR option. Mixing CIDR notation with +\fB-n\fR results in an error. This option can be specified zero (for defaults) to two times (once for IPv4, once for IPv6). By default, assigned IPv4 and IPv6 addresses are taken from the host interfaces @@ -172,10 +176,13 @@ is assigned for IPv4, and no additional address will be assigned for IPv6. .TP .BR \-n ", " \-\-netmask " " \fImask Assign IPv4 netmask \fImask\fR, expressed as dot-decimal or number of bits, via -DHCP (option 1). -By default, the netmask associated to the host address matching the assigned one -is used. If there's no matching address on the host, the netmask is determined -according to the CIDR block of the assigned address (RFC 4632). +DHCP (option 1). Alternatively, the prefix length can be specified using CIDR +notation with the \fB-a\fR, \fB--address\fR option (e.g. \fB-a\fR 192.0.2.1/24). +Mixing \fB-n\fR with CIDR notation results in an error. +If no address is indicated, the netmask associated with the adopted host address, +if any, is used. If an address is indicated, but without a prefix length, the +netmask is determined based on the corresponding network class. In all other +cases, the netmask is determined by using the indicated prefix length.
.TP .BR \-M ", " \-\-mac-addr " " \fIaddr -- 2.52.0
-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson