[Devel] [PATCH RHEL8 COMMIT] ms/mm: mempolicy: require at least one nodeid for MPOL_PREFERRED

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-193.6.3.vz8.4.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-193.6.3.vz8.4.9
------>
commit 56a5186d29d7373d71fd1519d90b785585840a2f
Author: Randy Dunlap <rdunlap at infradead.org>
Date:   Wed Apr 1 21:10:58 2020 -0700

    ms/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.
    
    Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display")
    Reported-by: Entropy Moe <3ntr0py1337 at gmail.com>
    Reported-by: syzbot+b055b1a6b2b958707a21 at syzkaller.appspotmail.com
    Signed-off-by: Randy Dunlap <rdunlap at infradead.org>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Tested-by: syzbot+b055b1a6b2b958707a21 at syzkaller.appspotmail.com
    Cc: Lee Schermerhorn <lee.schermerhorn at hp.com>
    Link: http://lkml.kernel.org/r/89526377-7eb6-b662-e1d8-4430928abde9@infradead.org
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-120642
    CVE-2020-11565: out-of-bounds write in mpol_parse_str function in mm/mempolicy.c
    
    (cherry picked from commit aa9f7d5172fac9bf1f09e678c35e287a40a7b7dd)
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 mm/mempolicy.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index dab3b16534f0..b24738101414 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2797,7 +2797,9 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
 	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;
@@ -2805,6 +2807,8 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
 				rest++;
 			if (*rest)
 				goto out;
+			if (nodes_empty(nodes))
+				goto out;
 		}
 		break;
 	case MPOL_INTERLEAVE: