Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 5.4 160/184] Revert 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op") | Date | Mon, 10 May 2021 12:20:54 +0200 |
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From: Thomas Gleixner <tglx@linutronix.de>
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: 337f13046ff0 ("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> --- kernel/futex.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/kernel/futex.c +++ b/kernel/futex.c @@ -3862,8 +3862,7 @@ long do_futex(u32 __user *uaddr, int op, 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; }
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