[tip: timers/core] timers: Mask invalid flags in do_init_timer()

["tip-bot2 for Qianli Zhao" <tip-bot2@linutronix.de>]

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

Commit-ID:     b952caf2d5ca898cc10d63be7722ae7a5daca696
Gitweb:        https://git.kernel.org/tip/b952caf2d5ca898cc10d63be7722ae7a5daca696
Author:        Qianli Zhao <zhaoqianli@xiaomi.com>
AuthorDate:    Thu, 13 Aug 2020 23:03:14 +08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 24 Sep 2020 22:12:18 +02:00

timers: Mask invalid flags in do_init_timer()

do_init_timer() accepts any combination of timer flags handed in by the
caller without a sanity check, but only TIMER_DEFFERABLE, TIMER_PINNED and
TIMER_IRQSAFE are valid.

If the supplied flags have other bits set, this could result in
malfunction. If bits are set in TIMER_CPUMASK the first timer usage could
deference a cpu base which is outside the range of possible CPUs. If
TIMER_MIGRATION is set, then the switch_timer_base() will live lock.

Prevent that with a sanity check which warns when invalid flags are
supplied and masks them out.

[ tglx: Made it WARN_ON_ONCE() and added context to the changelog ]

Signed-off-by: Qianli Zhao <zhaoqianli@xiaomi.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/9d79a8aa4eb56713af7379f99f062dedabcde140.1597326756.git.zhaoqianli@xiaomi.com
---
 include/linux/timer.h | 1 +
 kernel/time/timer.c   | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 07910ae..d10bc7e 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -67,6 +67,7 @@ struct timer_list {
 #define TIMER_DEFERRABLE	0x00080000
 #define TIMER_PINNED		0x00100000
 #define TIMER_IRQSAFE		0x00200000
+#define TIMER_INIT_FLAGS	(TIMER_DEFERRABLE | TIMER_PINNED | TIMER_IRQSAFE)
 #define TIMER_ARRAYSHIFT	22
 #define TIMER_ARRAYMASK		0xFFC00000
 
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a16764b..25e048d 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -794,6 +794,8 @@ static void do_init_timer(struct timer_list *timer,
 {
 	timer->entry.pprev = NULL;
 	timer->function = func;
+	if (WARN_ON_ONCE(flags & ~TIMER_INIT_FLAGS))
+		flags &= TIMER_INIT_FLAGS;
 	timer->flags = flags | raw_smp_processor_id();
 	lockdep_init_map(&timer->lockdep_map, name, key, 0);
 }