diff options
author | Oleg Nesterov <oleg@redhat.com> | 2010-05-26 23:42:54 +0200 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-05-27 18:12:44 +0200 |
commit | 065add3941bdca54fe04ed3471a96bce9af88793 (patch) | |
tree | 0c3505a04bb1b54926c527644c0ee2f57680c250 /kernel/signal.c | |
parent | ptrace: PTRACE_GETFDPIC: fix the unsafe usage of child->mm (diff) | |
download | linux-065add3941bdca54fe04ed3471a96bce9af88793.tar.xz linux-065add3941bdca54fe04ed3471a96bce9af88793.zip |
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>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r-- | kernel/signal.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/signal.c b/kernel/signal.c index 825a3f24ad76..2ee9573ed11f 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -642,7 +642,7 @@ static inline bool si_fromuser(const struct siginfo *info) static int check_kill_permission(int sig, struct siginfo *info, struct task_struct *t) { - const struct cred *cred = current_cred(), *tcred; + const struct cred *cred, *tcred; struct pid *sid; int error; @@ -656,8 +656,10 @@ static int check_kill_permission(int sig, struct siginfo *info, if (error) return error; + cred = current_cred(); tcred = __task_cred(t); - if ((cred->euid ^ tcred->suid) && + if (!same_thread_group(current, t) && + (cred->euid ^ tcred->suid) && (cred->euid ^ tcred->uid) && (cred->uid ^ tcred->suid) && (cred->uid ^ tcred->uid) && |