Messages in this thread Patch in this message | | | From | Kamal Mostafa <> | Subject | [PATCH 89/93] pidns: fix vfork() after unshare(CLONE_NEWPID) | Date | Fri, 20 Sep 2013 13:09:24 -0700 |
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3.8.13.10 -stable review patch. If anyone has any objections, please let me know.
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From: Oleg Nesterov <oleg@redhat.com>
commit e79f525e99b04390ca4d2366309545a836c03bf1 upstream.
Commit 8382fcac1b81 ("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 <oleg@redhat.com> Reported-by: Colin Walters <walters@redhat.com> Acked-by: Andy Lutomirski <luto@amacapital.net> Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [ kamal: backport to 3.8 (context) ] Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- kernel/fork.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 1c53e38..5c992f8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1170,10 +1170,11 @@ static struct task_struct *copy_process(unsigned long clone_flags, 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)) return ERR_PTR(-EINVAL); -- 1.8.1.2
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