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Subject[PATCH] mm: mempolicy: require at least one nodeid for MPOL_PREFERRED
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From: Randy Dunlap <rdunlap@infradead.org>

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>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
---
mm/mempolicy.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- lnx-56-rc6.orig/mm/mempolicy.c
+++ lnx-56-rc6/mm/mempolicy.c
@@ -2841,7 +2841,9 @@ 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;
@@ -2849,6 +2851,8 @@ int mpol_parse_str(char *str, struct mem
rest++;
if (*rest)
goto out;
+ if (nodes_empty(nodes))
+ goto out;
}
break;
case MPOL_INTERLEAVE:
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