diff options
authorThomas Gleixner <tglx@linutronix.de>2014-06-03 12:27:06 +0000
committerWilly Tarreau <w@1wt.eu>2014-06-19 00:25:58 +0200
commit523b5a514d29a8fdca8c26b7e41aa7d445e4ab0d (patch)
parent61b2412260ddff25ec54805df83627980d4c0bf9 (diff)
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. ] Signed-off-by: Darren Hart <dvhart@linux.intel.com> Cc: Kees Cook <keescook@chromium.org> Cc: Will Drewry <wad@chromium.org> Cc: stable@vger.kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> (cherry picked from commit b3eaa9fc5cd0a4d74b18f6b8dc617aeaf1873270) Signed-off-by: Willy Tarreau <w@1wt.eu>
1 files changed, 11 insertions, 3 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index c894eabaca2d..f77a94541f94 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -708,10 +708,18 @@ 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;