mm: mempolicy: require at least one nodeid for MPOL_PREFERRED (CVE-2020-11565)

debian/changelog

@@ -5,6 +5,8 @@ linux (4.19.98-1+deb10u1) UNRELEASED; urgency=medium
     (CVE-2020-8428)
   * vfs: fix do_last() regression
   * vhost: Check docket sk_family instead of call getname (CVE-2020-10942)
+  * mm: mempolicy: require at least one nodeid for MPOL_PREFERRED
+    (CVE-2020-11565)
 
  -- Salvatore Bonaccorso <carnil@debian.org>  Sun, 26 Apr 2020 20:32:58 +0200
 

debian/patches/bugfix/all/mm-mempolicy-require-at-least-one-nodeid-for-MPOL_PR.patch

@@ -0,0 +1,56 @@
+From: Randy Dunlap <rdunlap@infradead.org>
+Date: Wed, 1 Apr 2020 21:10:58 -0700
+Subject: mm: mempolicy: require at least one nodeid for MPOL_PREFERRED
+Origin: https://git.kernel.org/linus/aa9f7d5172fac9bf1f09e678c35e287a40a7b7dd
+Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-11565
+
+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>
+---
+ mm/mempolicy.c | 6 +++++-
+ 1 file changed, 5 insertions(+), 1 deletion(-)
+
+diff --git a/mm/mempolicy.c b/mm/mempolicy.c
+index 460683bbe58c..5fb427aed612 100644
+--- a/mm/mempolicy.c
++++ b/mm/mempolicy.c
+@@ -2898,7 +2898,9 @@ 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;
+@@ -2906,6 +2908,8 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
+ 				rest++;
+ 			if (*rest)
+ 				goto out;
++			if (nodes_empty(nodes))
++				goto out;
+ 		}
+ 		break;
+ 	case MPOL_INTERLEAVE:
+-- 
+2.26.2
+

debian/patches/series

@@ -308,6 +308,7 @@ bugfix/x86/KVM-nVMX-Don-t-emulate-instructions-in-guest-mode.patch
 bugfix/all/do_last-fetch-directory-i_mode-and-i_uid-before-it-s.patch
 bugfix/all/vfs-fix-do_last-regression.patch
 bugfix/all/vhost-Check-docket-sk_family-instead-of-call-getname.patch
+bugfix/all/mm-mempolicy-require-at-least-one-nodeid-for-MPOL_PR.patch
 
 # Backported change to provide boot-time entropy
 bugfix/all/random-try-to-actively-add-entropy-rather-than-passi.patch