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time: Verify time values in adjtimex ADJ_SETOFFSET to avoid overflow

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For adjtimex()'s ADJ_SETOFFSET, make sure the tv_usec value is
sane. We might multiply them later which can cause an overflow
and undefined behavior.

This patch introduces new helper functions to simplify the
checking code and adds comments to clarify

Orginally this patch was by Sasha Levin, but I've basically
rewritten it, so he should get credit for finding the issue
and I should get the blame for any mistakes made since.

Also, credit to Richard Cochran for the phrasing used in the
comment for what is considered valid here.

Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
This commit is contained in:
John Stultz 2015-12-03 22:09:31 -05:00
parent 52d189f1b3
commit 37cf4dc337
3 changed files with 35 additions and 3 deletions
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10
kernel/time/ntp.c
View file

@ -676,8 +676,14 @@ int ntp_validate_timex(struct timex *txc)
return -EINVAL;
}
if ((txc->modes & ADJ_SETOFFSET) && (!capable(CAP_SYS_TIME)))
return -EPERM;
if (txc->modes & ADJ_SETOFFSET) {
/* In order to inject time, you gotta be super-user! */
if (!capable(CAP_SYS_TIME))
return -EPERM;
if (!timeval_inject_offset_valid(&txc->time))
return -EINVAL;
}
/*
* Check for potential multiplication overflows that can