From: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> 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/89526377-7eb6-b662-e1d8-4430928abde9@xxxxxxxxxxxxx Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display") Reported-by: Entropy Moe <3ntr0py1337@xxxxxxxxx> Reported-by: syzbot+b055b1a6b2b958707a21@xxxxxxxxxxxxxxxxxxxxxxxxx Tested-by: syzbot+b055b1a6b2b958707a21@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/mempolicy.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- 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: _
