Commit 4fbf5d68 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

Revert 337f1304 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op") 



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: 337f1304 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op")
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210422194704.834797921@linutronix.de
parent 28ce0e70

kernel/futex.c

+1 −2
Original line number Diff line number Diff line
@@ -3710,8 +3710,7 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, 


	if (op & FUTEX_CLOCK_REALTIME) {

		flags |= FLAGS_CLOCKRT;

		if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \

		    cmd != FUTEX_WAIT_REQUEUE_PI)

		if (cmd != FUTEX_WAIT_BITSET &&	cmd != FUTEX_WAIT_REQUEUE_PI)

			return -ENOSYS;

	}