[137/155] mm: mempolicy: require at least one nodeid for MPOL_PREFERRED

Commit Message

Andrew Morton April 2, 2020, 4:10 a.m. UTC

From: Randy Dunlap <[e-mail]>
Subject: mm: mempolicy: require at least one nodeid for MPOL_PREFERRED

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.

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display")
Reported-by: Entropy Moe <[e-mail]>
Reported-by: [e-mail]
Tested-by: [e-mail]
Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Lee Schermerhorn <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/mempolicy.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Patch

--- a/mm/mempolicy.c~mm-mempolicy-require-at-least-one-nodeid-for-mpol_preferred
+++ a/mm/mempolicy.c
@@ -2898,7 +2898,9 @@  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;
@@ -2906,6 +2908,8 @@  int mpol_parse_str(char *str, struct mem
 				rest++;
 			if (*rest)
 				goto out;
+			if (nodes_empty(nodes))
+				goto out;
 		}
 		break;
 	case MPOL_INTERLEAVE: