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Revert 337f13046f ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op")

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commit 4fbf5d6837bf81fd7a27d771358f4ee6c4f243f8 upstream.

The FUTEX_WAIT operand has historically a relative timeout which means that
the clock id is irrelevant as relative timeouts on CLOCK_REALTIME are not
subject to wall clock changes and therefore are mapped by the kernel to
CLOCK_MONOTONIC for simplicity.

If a caller would set FUTEX_CLOCK_REALTIME for FUTEX_WAIT the timeout is
still treated relative vs. CLOCK_MONOTONIC and then the wait arms that
timeout based on CLOCK_REALTIME which is broken and obviously has never
been used or even tested.

Reject any attempt to use FUTEX_CLOCK_REALTIME with FUTEX_WAIT again.

The desired functionality can be achieved with FUTEX_WAIT_BITSET and a
FUTEX_BITSET_MATCH_ANY argument.

Fixes: 337f13046f ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210422194704.834797921@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Thomas Gleixner 2021-04-22 21:44:18 +02:00 committed by Greg Kroah-Hartman
parent 2b040d13b4
commit 8d2be04dbb
1 changed files with 1 additions and 2 deletions
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3
kernel/futex.c
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@ -3862,8 +3862,7 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
if (op & FUTEX_CLOCK_REALTIME) { if (op & FUTEX_CLOCK_REALTIME) {
flags |= FLAGS_CLOCKRT; flags |= FLAGS_CLOCKRT;
if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \ if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
cmd != FUTEX_WAIT_REQUEUE_PI)
return -ENOSYS; return -ENOSYS;
} }