[PATCH 4.9 32/68] mm/mempolicy.c: fix out of bounds write in mpol_parse_str()

Greg Kroah-Hartman
2020-02-03T16:25:55Z

From: Dan Carpenter <dan.carpenter@oracle.com>

commit c7a91bc7c2e17e0a9c8b9745a2cb118891218fd1 upstream.

What we are trying to do is change the '=' character to a NUL terminator
and then at the end of the function we restore it back to an '='. The
problem is there are two error paths where we jump to the end of the
function before we have replaced the '=' with NUL.

We end up putting the '=' in the wrong place (possibly one element
before the start of the buffer).

Link: http://lkml.kernel.org/r/20200115055426.vdjwvry44nfug7yy@kili.mountain
Reported-by: syzbot+e64a13c5369a194d67df@syzkaller.appspotmail.com
Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Dmitry Vyukov <dvyukov@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/mempolicy.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2744,6 +2744,9 @@ int mpol_parse_str(char *str, struct mem
char *flags = strchr(str, '=');
int err = 1;

+ if (flags)
+ *flags++ = '\0'; /* terminate mode string */
+
if (nodelist) {
/* NUL-terminate mode or flags string */
*nodelist++ = '\0';
@@ -2754,9 +2757,6 @@ int mpol_parse_str(char *str, struct mem
} else
nodes_clear(nodes);

- if (flags)
- *flags++ = '\0'; /* terminate mode string */
-
for (mode = 0; mode < MPOL_MAX; mode++) {
if (!strcmp(str, policy_modes[mode])) {
break;