linux-kernel - Race Condition over sys

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Date:	Sat, 30 Sep 2006 08:53:24 +0800
From:	"Dong Feng" <middle.fengdong@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Race Condition over sys_tz

The operations on sys_tz, so far known to me in sys_settimeofday and
sys_gettimeofday, is neither atomic nor protected by any lock. I
suspect it probably causes unpredictable behavior when multiple
processes try to set the system time zone simultaneously.

Following is the code fragment extracted from do_sys_settimeofday().
The function is invoked by sys_settimeofday() without locking. At
least two non-atomic operations:

1. struct copy between *tz and sys_tz.
2. The test-and-operate over firsttime.

if (tz) {
        /* SMP safe, global irq locking makes it work. */
        sys_tz = *tz;
        if (firsttime) {
                firsttime = 0;
                if (!tv)
                        warp_clock();
        }
}
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