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authorOleg Nesterov <oleg@redhat.com>2010-05-26 14:42:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-27 09:12:44 -0700
commit065add3941bdca54fe04ed3471a96bce9af88793 (patch)
tree0c3505a04bb1b54926c527644c0ee2f57680c250 /fs/exec.c
parente0129ef91ed758c06b6557c36124acfb2e1c7305 (diff)
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signals: check_kill_permission(): don't check creds if same_thread_group()
Andrew Tridgell reports that aio_read(SIGEV_SIGNAL) can fail if the notification from the helper thread races with setresuid(), see http://samba.org/~tridge/junkcode/aio_uid.c This happens because check_kill_permission() doesn't permit sending a signal to the task with the different cred->xids. But there is not any security reason to check ->cred's when the task sends a signal (private or group-wide) to its sub-thread. Whatever we do, any thread can bypass all security checks and send SIGKILL to all threads, or it can block a signal SIG and do kill(gettid(), SIG) to deliver this signal to another sub-thread. Not to mention that CLONE_THREAD implies CLONE_VM. Change check_kill_permission() to avoid the credentials check when the sender and the target are from the same thread group. Also, move "cred = current_cred()" down to avoid calling get_current() twice. Note: David Howells pointed out we could relax this even more, the CLONE_SIGHAND (without CLONE_THREAD) case probably does not need these checks too. Roland said: : The glibc (libpthread) that does set*id across threads has : been in use for a while (2.3.4?), probably in distro's using kernels as old : or older than any active -stable streams. In the race in question, this : kernel bug is breaking valid POSIX application expectations. Reported-by: Andrew Tridgell <tridge@samba.org> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Roland McGrath <roland@redhat.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Eric Paris <eparis@parisplace.org> Cc: Jakub Jelinek <jakub@redhat.com> Cc: James Morris <jmorris@namei.org> Cc: Roland McGrath <roland@redhat.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: <stable@kernel.org> [all kernel versions] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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