This is a note to let you know that I've just added the patch titled
Revert 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op")
to the 5.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
revert-337f13046ff0-futex-allow-futex_clock_realtime-with-futex_wait-op.patch
and it can be found in the queue-5.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4fbf5d6837bf81fd7a27d771358f4ee6c4f243f8 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Thu, 22 Apr 2021 21:44:18 +0200
Subject: Revert 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op")
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20210422194704.834797921@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/futex.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3711,8 +3711,7 @@ 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;
}
Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are
queue-5.12/posix-timers-preserve-return-value-in-clock_adjtime32.patch
queue-5.12/futex-do-not-apply-time-namespace-adjustment-on-futex_lock_pi.patch
queue-5.12/revert-337f13046ff0-futex-allow-futex_clock_realtime-with-futex_wait-op.patch
queue-5.12/genirq-matrix-prevent-allocation-counter-corruption.patch
queue-5.12/x86-cpu-initialize-msr_tsc_aux-if-rdtscp-or-rdpid-is-supported.patch
