| Message ID | 20210422194704.834797921@linutronix.de |
|---|---|
| State | New |
| Headers | show |
| Series | [1/6] Revert 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op") | expand |
--- 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; }
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> Cc: stable@vger.kernel.org Cc: Darren Hart <dvhart@infradead.org> --- kernel/futex.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)