[PATCH v2] kernel: sysctl: ignore out-of-range taint bits introduced via kernel.tainted

[Rafael Aquini]

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=...'.
These interface, however, are open for any integer value
and this might 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 <aquini@xxxxxxxxxx>
---
Changelog:
v2: simplify the bit iterator within proc_taint(),
    and silently drop out-of-range bits                         (akpm)

 kernel/sysctl.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8a176d8727a3..fcd46fc41206 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2628,10 +2628,9 @@ static int proc_taint(struct ctl_table *table, int write,
 		 * to everyone's atomic.h for this
 		 */
 		int i;
-		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;
-- 
2.25.4