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pasta: Detach mount namespace, (re)mount procfs before spawning command

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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@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Stefano Brivio 2023-05-21 14:50:11 +02:00
parent b0881aae6d
commit b0e450aa85
1 changed files with 6 additions and 1 deletions
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7
pasta.c
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@ -29,6 +29,7 @@
#include <syslog.h> #include <syslog.h>
#include <sys/epoll.h> #include <sys/epoll.h>
#include <sys/inotify.h> #include <sys/inotify.h>
#include <sys/mount.h>
#include <sys/types.h> #include <sys/types.h>
#include <sys/stat.h> #include <sys/stat.h>
#include <fcntl.h> #include <fcntl.h>
@ -172,6 +173,10 @@ static int pasta_spawn_cmd(void *arg)
const struct pasta_spawn_cmd_arg *a; const struct pasta_spawn_cmd_arg *a;
sigset_t set; 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")) if (write_file("/proc/sys/net/ipv4/ping_group_range", "0 0"))
warn("Cannot set ping_group_range, ICMP requests might fail"); 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, pasta_child_pid = do_clone(pasta_spawn_cmd, ns_fn_stack,
sizeof(ns_fn_stack), sizeof(ns_fn_stack),
CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET | CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET |
CLONE_NEWUTS | SIGCHLD, CLONE_NEWUTS | CLONE_NEWNS | SIGCHLD,
(void *)&arg); (void *)&arg);
if (pasta_child_pid == -1) { if (pasta_child_pid == -1) {