linux-kernel - [RFC][PATCH -reworked] time: Verify time values in adjtimex ADJ

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Message-Id: <1449519118-4950-1-git-send-email-john.stultz@linaro.org>
Date:	Mon,  7 Dec 2015 12:11:58 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Richard Cochran <richardcochran@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>
Subject: [RFC][PATCH -reworked] time: Verify time values in adjtimex ADJ_SETOFFSET to avoid overflow

From: Sasha Levin <sasha.levin@...cle.com>

Make sure the tv_usec makes sense. We might multiply them later which can
cause an overflow and undefined behavior.

Cc: Sasha Levin <sasha.levin@...cle.com>
Cc: Richard Cochran <richardcochran@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
[jstultz: Moved corrected check to ntp_validate_timex]
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
Here's my attempt at reworking the patch.
Let me know if you have any thoughts or objections.
thanks
-john


 kernel/time/ntp.c         | 14 ++++++++++++--
 kernel/time/timekeeping.c |  1 +
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 36616c3..e9a1874 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -676,8 +676,18 @@ 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;
+
+		/*
+		 * tv_sec can be positive or negative, but usec
+		 * must be positive and from 0->USEC_PER_SEC
+		 */
+		if (txc->time.tv_usec >= USEC_PER_SEC)
+			return -EINVAL;
+	}
 
 	/*
 	 * Check for potential multiplication overflows that can
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 99188ee..a37222b 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1986,6 +1986,7 @@ int do_adjtimex(struct timex *txc)
 
 	if (txc->modes & ADJ_SETOFFSET) {
 		struct timespec delta;
+
 		delta.tv_sec  = txc->time.tv_sec;
 		delta.tv_nsec = txc->time.tv_usec;
 		if (!(txc->modes & ADJ_NANO))
-- 
1.9.1

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