From: Oleg Nesterov <[email protected]>
Subject: pidns: fix vfork() after unshare(CLONE_NEWPID)
8382fcac ("pidns: Outlaw thread creation after unshare(CLONE_NEWPID)")
nacks CLONE_VM if the forking process unshared pid_ns, this obviously
breaks vfork:
int main(void)
{
assert(unshare(CLONE_NEWUSER | CLONE_NEWPID) == 0);
assert(vfork() >= 0);
_exit(0);
return 0;
}
fails without this patch.
Change this check to use CLONE_SIGHAND instead. This also forbids
CLONE_THREAD automatically, and this is what the comment implies.
We could probably even drop CLONE_SIGHAND and use CLONE_THREAD, but it
would be safer to not do this. The current check denies CLONE_SIGHAND
implicitely and there is no reason to change this.
Eric said "CLONE_SIGHAND is fine. CLONE_THREAD would be even better.
Having shared signal handling between two different pid namespaces is the
case that we are fundamentally guarding against."
Signed-off-by: Oleg Nesterov <[email protected]>
Reported-by: Colin Walters <[email protected]>
Acked-by: Andy Lutomirski <[email protected]>
Reviewed-by: "Eric W. Biederman" <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
kernel/fork.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff -puN kernel/fork.c~pidns-fix-vfork-after-unshareclone_newpid kernel/fork.c
--- a/kernel/fork.c~pidns-fix-vfork-after-unshareclone_newpid
+++ a/kernel/fork.c
@@ -1173,10 +1173,11 @@ static struct task_struct *copy_process(
return ERR_PTR(-EINVAL);
/*
- * If the new process will be in a different pid namespace
- * don't allow the creation of threads.
+ * If the new process will be in a different pid namespace don't
+ * allow it to share a thread group or signal handlers with the
+ * forking task.
*/
- if ((clone_flags & (CLONE_VM|CLONE_NEWPID)) &&
+ if ((clone_flags & (CLONE_SIGHAND | CLONE_NEWPID)) &&
(task_active_pid_ns(current) !=
current->nsproxy->pid_ns_for_children))
return ERR_PTR(-EINVAL);
_
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