From 0847675b78e0c9643c1fb82782db095b9b118510 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 3 Jun 2014 12:27:06 +0000 Subject: [PATCH] futex: Validate atomic acquisition in futex_lock_pi_atomic() We need to protect the atomic acquisition in the kernel against rogue user space which sets the user space futex to 0, so the kernel side acquisition succeeds while there is existing state in the kernel associated to the real owner. Verify whether the futex has waiters associated with kernel state. If it has, return -EINVAL. The state is corrupted already, so no point in cleaning it up. Subsequent calls will fail as well. Not our problem. [ tglx: Use futex_top_waiter() and explain why we do not need to try restoring the already corrupted user space state. ] Change-Id: I5eb84a6483b6e2ddeac70e9b82e69b63af45b189 Signed-off-by: Darren Hart Cc: Kees Cook Cc: Will Drewry Cc: stable@vger.kernel.org Signed-off-by: Thomas Gleixner Signed-off-by: Linus Torvalds --- kernel/futex.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 553c383e9e34..578366668c82 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -748,10 +748,18 @@ retry: return -EDEADLK; /* - * Surprise - we got the lock. Just return to userspace: + * Surprise - we got the lock, but we do not trust user space at all. */ - if (unlikely(!curval)) - return 1; + if (unlikely(!curval)) { + /* + * We verify whether there is kernel state for this + * futex. If not, we can safely assume, that the 0 -> + * TID transition is correct. If state exists, we do + * not bother to fixup the user space state as it was + * corrupted already. + */ + return futex_top_waiter(hb, key) ? -EINVAL : 1; + } uval = curval; -- 2.34.1