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authorThomas Gleixner <tglx@linutronix.de>2014-06-03 12:27:06 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-06-07 13:25:40 -0700
commit63d6ad59dd43f44249150aa8c72eeb01bbe0a599 (patch)
tree4acb4b586b4e9271ab73c65358d76a5a7330ebcb
parentb58623fb64ff0454ec20bce7a02275a20c23086d (diff)
downloadlinux-linaro-stable-63d6ad59dd43f44249150aa8c72eeb01bbe0a599.tar.gz
futex: Validate atomic acquisition in futex_lock_pi_atomic()
commit b3eaa9fc5cd0a4d74b18f6b8dc617aeaf1873270 upstream. 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. ] Signed-off-by: Darren Hart <dvhart@linux.intel.com> Cc: Kees Cook <keescook@chromium.org> Cc: Will Drewry <wad@chromium.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/futex.c14
1 files changed, 11 insertions, 3 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 93e522fa0e0f..8c1e6d086306 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -762,10 +762,18 @@ 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;