[PATCH 3.16 226/245] mm: mempolicy: require at least one nodeid for MPOL_PREFERRED

Ben Hutchings
2020-04-23T23:08:51Z

From: Randy Dunlap <rdunlap@infradead.org>

commit aa9f7d5172fac9bf1f09e678c35e287a40a7b7dd upstream.

Using an empty (malformed) nodelist that is not caught during mount option
parsing leads to a stack-out-of-bounds access.

The option string that was used was: "mpol=prefer:,". However,
MPOL_PREFERRED requires a single node number, which is not being provided
here.

Add a check that 'nodes' is not empty after parsing for MPOL_PREFERRED's
nodeid.

Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display")
Reported-by: Entropy Moe <3ntr0py1337@gmail.com>
Reported-by: syzbot+b055b1a6b2b958707a21@syzkaller.appspotmail.com
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: syzbot+b055b1a6b2b958707a21@syzkaller.appspotmail.com
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Link: http://lkml.kernel.org/r/89526377-7eb6-b662-e1d8-4430928abde9@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
mm/mempolicy.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2711,7 +2711,9 @@ int mpol_parse_str(char *str, struct mem
switch (mode) {
case MPOL_PREFERRED:
/*
- * Insist on a nodelist of one node only
+ * Insist on a nodelist of one node only, although later
+ * we use first_node(nodes) to grab a single node, so here
+ * nodelist (or nodes) cannot be empty.
*/
if (nodelist) {
char *rest = nodelist;
@@ -2719,6 +2721,8 @@ int mpol_parse_str(char *str, struct mem
rest++;
if (*rest)
goto out;
+ if (nodes_empty(nodes))
+ goto out;
}
break;