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 <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Link: http://lkml.kernel.org/r/20200512223946.888020-1-aquini@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index f69d581..db1ce7a 100644 (file)
--- 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;