linux-kernel - Re: [BUG] Null pointer deref with hrtimer_try_to

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Date:	Sat, 20 Dec 2008 21:27:34 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Eric Sesterhenn <snakebyte@....de>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	John Stultz <johnstul@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [BUG] Null pointer deref with hrtimer_try_to_cancel()

Impact: Prevent kernel crash with posix timer clockid CLOCK_MONOTONIC_RAW

commit 2d42244ae71d6c7b0884b5664cf2eda30fb2ae68 (clocksource:
introduce CLOCK_MONOTONIC_RAW) introduced a new clockid, which is only
available to read out the raw not NTP adjusted system time.

The above commit did not prevent that a posix timer can be created
with that clockid. The timer_create() syscall succeeds and initializes
the timer to a non existing hrtimer base. When the timer is deleted
either by timer_delete() or by the exit() cleanup the kernel crashes.

Prevent the creation of timers for CLOCK_MONOTONIC_RAW by setting the
posix clock function to no_timer_create which returns an error code.

Reported-by: Eric Sesterhenn <snakebyte@....de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 5e79c66..a140e44 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -197,6 +197,11 @@ static int common_timer_create(struct k_itimer *new_timer)
 	return 0;
 }
 
+static int no_timer_create(struct k_itimer *new_timer)
+{
+	return -EOPNOTSUPP;
+}
+
 /*
  * Return nonzero if we know a priori this clockid_t value is bogus.
  */
@@ -248,6 +253,7 @@ static __init int init_posix_timers(void)
 		.clock_getres = hrtimer_get_res,
 		.clock_get = posix_get_monotonic_raw,
 		.clock_set = do_posix_clock_nosettime,
+		.timer_create = no_timer_create,
 	};
 
 	register_posix_clock(CLOCK_REALTIME, &clock_realtime);
--
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