kernel/sysctl.c: ignore out-of-range taint bits introduced via kernel.tainted

Users with SYS_ADMIN capability can add arbitrary taint flags to the
running kernel by writing to /proc/sys/kernel/tainted or issuing the
command 'sysctl -w kernel.tainted=...'.  This interface, however, is
open for any integer value and this might cause an invalid set of flags
being committed to the tainted_mask bitset.

This patch introduces a simple way for proc_taint() to ignore any
eventual invalid bit coming from the user input before committing those
bits to the kernel tainted_mask.

Signed-off-by: Rafael Aquini <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Luis Chamberlain <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Iurii Zaikin <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 2 insertions, 3 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index f69d581d39c3..db1ce7af2563 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -880,10 +880,9 @@ static int proc_taint(struct ctl_table *table, int write,
 		 * Poor man's atomic or. Not worth adding a primitive
 		 * to everyone's atomic.h for this
 		 */
-		for (i = 0; i < BITS_PER_LONG && tmptaint >> i; i++) {
-			if ((tmptaint >> i) & 1)
+		for (i = 0; i < TAINT_FLAGS_COUNT; i++)
+			if ((1UL << i) & tmptaint)
 				add_taint(i, LOCKDEP_STILL_OK);
-		}
 	}
 
 	return err;