[PATCH] ntp, security: fix non privileged system time shifting

[Richard Cochran]

The ADJ_SETOFFSET bit added in commit 094aa188 also introduced a way for
any user to change the system time. Sneaky or buggy calls to adjtimex()
could set

    ADJ_OFFSET_SS_READ | ADJ_SETOFFSET

which would result in a successful call to timekeeping_inject_offset().
This patch fixes the issue by adding the capability check.

Signed-off-by: Richard Cochran <richard.cochran@xxxxxxxxxx>
---
 kernel/time/ntp.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 35e68e3..5e65fd5 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -652,6 +652,8 @@ int do_adjtimex(struct timex *txc)
 		struct timespec delta;
 		delta.tv_sec  = txc->time.tv_sec;
 		delta.tv_nsec = txc->time.tv_usec;
+		if (!capable(CAP_SYS_TIME))
+			return -EPERM;
 		if (!(txc->modes & ADJ_NANO))
 			delta.tv_nsec *= 1000;
 		result = timekeeping_inject_offset(&delta);
-- 
1.7.0.4

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