[003/118] mm/mempolicy.c: fix out of bounds write in mpol_parse_str()

Commit Message

Andrew Morton Jan. 31, 2020, 6:11 a.m. UTC

From: Dan Carpenter <[e-mail]>
Subject: mm/mempolicy.c: fix out of bounds write in mpol_parse_str()

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/[e-mail]
Reported-by: [e-mail]
Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display")
Signed-off-by: Dan Carpenter <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Dmitry Vyukov <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Dan Carpenter <[e-mail]>
Cc: Lee Schermerhorn <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- a/mm/mempolicy.c~mm-mempolicyc-fix-out-of-bounds-write-in-mpol_parse_str
+++ a/mm/mempolicy.c
@@ -2821,6 +2821,9 @@  int mpol_parse_str(char *str, struct mem
 	char *flags = strchr(str, '=');
 	int err = 1, mode;
 
+	if (flags)
+		*flags++ = '\0';	/* terminate mode string */
+
 	if (nodelist) {
 		/* NUL-terminate mode or flags string */
 		*nodelist++ = '\0';
@@ -2831,9 +2834,6 @@  int mpol_parse_str(char *str, struct mem
 	} else
 		nodes_clear(nodes);
 
-	if (flags)
-		*flags++ = '\0';	/* terminate mode string */
-
 	mode = match_string(policy_modes, MPOL_MAX, str);
 	if (mode < 0)
 		goto out;