From: Oleg Nesterov Date: Wed, 26 May 2010 21:42:54 +0000 (-0700) Subject: signals: check_kill_permission(): don't check creds if same_thread_group() X-Git-Tag: v2.6.35-rc1~184 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=065add3941bdca54fe04ed3471a96bce9af88793;p=pandora-kernel.git 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 Signed-off-by: Oleg Nesterov Acked-by: Roland McGrath Acked-by: David Howells Cc: Eric Paris Cc: Jakub Jelinek Cc: James Morris Cc: Roland McGrath Cc: Stephen Smalley Cc: [all kernel versions] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed