On Mon, May 22, 2023 at 01:41:57AM +0200, Stefano Brivio wrote:If we want /proc contents to be consistent after pasta spawns a child process in a new PID namespace (only for operation without a pre-existing namespace), we need to mount /proc after the clone(2) call with CLONE_NEWPID, and we enable the child to do that by passing, in the same call, the CLONE_NEWNS flag, as described by pid_namespaces(7). This is not really a remount: in fact, passing MS_REMOUNT to mount(2) would make the call fail. We're in another mount namespace now, so it's a fresh mount that has the effect of hiding the existing one. Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>Reviewed-by: David Gibson <david(a)gibson.dropbear.id.au>--- pasta.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/pasta.c b/pasta.c index 3a4d704..b30ce70 100644 --- a/pasta.c +++ b/pasta.c @@ -29,6 +29,7 @@ #include <syslog.h> #include <sys/epoll.h> #include <sys/inotify.h> +#include <sys/mount.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> @@ -172,6 +173,10 @@ static int pasta_spawn_cmd(void *arg) const struct pasta_spawn_cmd_arg *a; sigset_t set; + /* We run in a detached PID and mount namespace: mount /proc over */ + if (mount("", "/proc", "proc", 0, NULL)) + warn("Couldn't mount /proc: %s", strerror(errno)); + if (write_file("/proc/sys/net/ipv4/ping_group_range", "0 0")) warn("Cannot set ping_group_range, ICMP requests might fail"); @@ -243,7 +248,7 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid, pasta_child_pid = do_clone(pasta_spawn_cmd, ns_fn_stack, sizeof(ns_fn_stack), CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET | - CLONE_NEWUTS | SIGCHLD, + CLONE_NEWUTS | CLONE_NEWNS | SIGCHLD, (void *)&arg); if (pasta_child_pid == -1) {-- David Gibson | 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