[tip: timers/urgent] posix-cpu-timers: Prevent spuriously armed 0-value itimer

[tip-bot2 for Frederic Weisbecker]

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     8cd9da85d2bd87ce889043e7b1735723dd10eb89
Gitweb:        https://git.kernel.org/tip/8cd9da85d2bd87ce889043e7b1735723dd10eb89
Author:        Frederic Weisbecker <frederic@xxxxxxxxxx>
AuthorDate:    Mon, 13 Sep 2021 16:53:32 +02:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Thu, 23 Sep 2021 11:53:51 +02:00

posix-cpu-timers: Prevent spuriously armed 0-value itimer

Resetting/stopping an itimer eventually leads to it being reprogrammed
with an actual "0" value. As a result the itimer expires on the next
tick, triggering an unexpected signal.

To fix this, make sure that
struct signal_struct::it[CPUCLOCK_PROF/VIRT]::expires is set to 0 when
setitimer() passes a 0 it_value, indicating that the timer must stop.

Fixes: 406dd42bd1ba ("posix-cpu-timers: Force next expiration recalc after itimer reset")
Reported-by: Victor Stinner <vstinner@xxxxxxxxxx>
Reported-by: Chris Hixon <linux-kernel-bugs@xxxxxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210913145332.232023-1-frederic@xxxxxxxxxx
---
 kernel/time/posix-cpu-timers.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index ee73686..643d412 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1404,7 +1404,8 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
 			}
 		}
 
-		*newval += now;
+		if (*newval)
+			*newval += now;
 	}
 
 	/*