posix-cpu-timers: Sanitize bogus WARNONS

BugLink: https://bugs.launchpad.net/bugs/1847155
[ Upstream commit 692117c1f7a6770ed41dd8f277cd9fed1dfb16f1 ]

Warning when p == NULL and then proceeding and dereferencing p does not
make any sense as the kernel will crash with a NULL pointer dereference
right away.

Bailing out when p == NULL and returning an error code does not cure the
underlying problem which caused p to be NULL. Though it might allow to
do proper debugging.

Same applies to the clock id check in set_process_cpu_timer().

Clean them up and make them return without trying to do further damage.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190819143801.846497772@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 5d22cce5d49026dc96a14eca182333a969db9c34..dfde8d22b204fc97e3333e4e15701e02994148cc 100644 (file)
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -374,7 +374,8 @@ static int posix_cpu_timer_del(struct k_itimer *timer)
        struct sighand_struct *sighand;
        struct task_struct *p = timer->it.cpu.task;
 
-       WARN_ON_ONCE(p == NULL);
+       if (WARN_ON_ONCE(!p))
+               return -EINVAL;
 
        /*
         * Protect against sighand release/switch in exit/exec and process/
@@ -579,7 +580,8 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
        u64 old_expires, new_expires, old_incr, val;
        int ret;
 
-       WARN_ON_ONCE(p == NULL);
+       if (WARN_ON_ONCE(!p))
+               return -EINVAL;
 
        /*
         * Use the to_ktime conversion because that clamps the maximum
@@ -716,10 +718,11 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 
 static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)
 {
-       u64 now;
        struct task_struct *p = timer->it.cpu.task;
+       u64 now;
 
-       WARN_ON_ONCE(p == NULL);
+       if (WARN_ON_ONCE(!p))
+               return;
 
        /*
         * Easy part: convert the reload time.
@@ -990,12 +993,13 @@ static void check_process_timers(struct task_struct *tsk,
  */
 static void posix_cpu_timer_rearm(struct k_itimer *timer)
 {
+       struct task_struct *p = timer->it.cpu.task;
        struct sighand_struct *sighand;
        unsigned long flags;
-       struct task_struct *p = timer->it.cpu.task;
        u64 now;
 
-       WARN_ON_ONCE(p == NULL);
+       if (WARN_ON_ONCE(!p))
+               return;
 
        /*
         * Fetch the current sample and update the timer's expiry time.
@@ -1189,7 +1193,9 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
 {
        u64 now;
 
-       WARN_ON_ONCE(clock_idx == CPUCLOCK_SCHED);
+       if (WARN_ON_ONCE(clock_idx >= CPUCLOCK_SCHED))
+               return;
+
        cpu_timer_sample_group(clock_idx, tsk, &now);
 
        if (oldval) {