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Subject[PATCH] futex: Check for uaddr alignment as early as possible
Date
From: "Darren Hart (VMware)" <dvhart@infradead.org>

uaddr alignment is currently tested by get_futex_key(). We can catch
misalignment earlier in sys_futex and return -EINVAL sooner. This
simplifies get_futex_key() a little, but more importantly exits the
kernel as soon as an invalid parameter is detected.

Passes all selftests/futex testcases on a dual socket Xeon E5-2670, 16
physical cores total, 32 threads total.

Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
---
kernel/futex.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 76ed592..c3ee6c4 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -509,8 +509,6 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
* The futex address must be "naturally" aligned.
*/
key->both.offset = address % PAGE_SIZE;
- if (unlikely((address % sizeof(u32)) != 0))
- return -EINVAL;
address -= key->both.offset;

if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
@@ -3525,6 +3523,11 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
u32 val2 = 0;
int cmd = op & FUTEX_CMD_MASK;

+ /* Only allow for aligned uaddr variables */
+ if (unlikely((unsigned long)uaddr % sizeof(u32) != 0 ||
+ (unsigned long)uaddr2 % sizeof(u32) != 0))
+ return -EINVAL;
+
if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
cmd == FUTEX_WAIT_BITSET ||
cmd == FUTEX_WAIT_REQUEUE_PI)) {
--
2.9.4
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