mm/mempolicy: do not allow illegal MPOL_F_NUMA_BALANCING | MPOL_LOCAL in mbind()

syzbot reported access to unitialized memory in mbind() [1]

Issue came with commit bda420b98505 ("numa balancing: migrate on fault
among multiple bound nodes")

This commit added a new bit in MPOL_MODE_FLAGS, but only checked valid
combination (MPOL_F_NUMA_BALANCING can only be used with MPOL_BIND) in
do_set_mempolicy()

This patch moves the check in sanitize_mpol_flags() so that it is also
used by mbind()

  [1]
  BUG: KMSAN: uninit-value in __mpol_equal+0x567/0x590 mm/mempolicy.c:2260
   __mpol_equal+0x567/0x590 mm/mempolicy.c:2260
   mpol_equal include/linux/mempolicy.h:105 [inline]
   vma_merge+0x4a1/0x1e60 mm/mmap.c:1190
   mbind_range+0xcc8/0x1e80 mm/mempolicy.c:811
   do_mbind+0xf42/0x15f0 mm/mempolicy.c:1333
   kernel_mbind mm/mempolicy.c:1483 [inline]
   __do_sys_mbind mm/mempolicy.c:1490 [inline]
   __se_sys_mbind+0x437/0xb80 mm/mempolicy.c:1486
   __x64_sys_mbind+0x19d/0x200 mm/mempolicy.c:1486
   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
   do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:82
   entry_SYSCALL_64_after_hwframe+0x44/0xae

  Uninit was created at:
   slab_alloc_node mm/slub.c:3221 [inline]
   slab_alloc mm/slub.c:3230 [inline]
   kmem_cache_alloc+0x751/0xff0 mm/slub.c:3235
   mpol_new mm/mempolicy.c:293 [inline]
   do_mbind+0x912/0x15f0 mm/mempolicy.c:1289
   kernel_mbind mm/mempolicy.c:1483 [inline]
   __do_sys_mbind mm/mempolicy.c:1490 [inline]
   __se_sys_mbind+0x437/0xb80 mm/mempolicy.c:1486
   __x64_sys_mbind+0x19d/0x200 mm/mempolicy.c:1486
   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
   do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:82
   entry_SYSCALL_64_after_hwframe+0x44/0xae
  =====================================================
  Kernel panic - not syncing: panic_on_kmsan set ...
  CPU: 0 PID: 15049 Comm: syz-executor.0 Tainted: G    B             5.15.0-rc2-syzkaller #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
  Call Trace:
   __dump_stack lib/dump_stack.c:88 [inline]
   dump_stack_lvl+0x1ff/0x28e lib/dump_stack.c:106
   dump_stack+0x25/0x28 lib/dump_stack.c:113
   panic+0x44f/0xdeb kernel/panic.c:232
   kmsan_report+0x2ee/0x300 mm/kmsan/report.c:186
   __msan_warning+0xd7/0x150 mm/kmsan/instrumentation.c:208
   __mpol_equal+0x567/0x590 mm/mempolicy.c:2260
   mpol_equal include/linux/mempolicy.h:105 [inline]
   vma_merge+0x4a1/0x1e60 mm/mmap.c:1190
   mbind_range+0xcc8/0x1e80 mm/mempolicy.c:811
   do_mbind+0xf42/0x15f0 mm/mempolicy.c:1333
   kernel_mbind mm/mempolicy.c:1483 [inline]
   __do_sys_mbind mm/mempolicy.c:1490 [inline]
   __se_sys_mbind+0x437/0xb80 mm/mempolicy.c:1486
   __x64_sys_mbind+0x19d/0x200 mm/mempolicy.c:1486
   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
   do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:82
   entry_SYSCALL_64_after_hwframe+0x44/0xae

Link: https://lkml.kernel.org/r/20211001215630.810592-1-eric.dumazet@gmail.com
Fixes: bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 1592b08..d12e060 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -856,16 +856,6 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
                goto out;
        }
 
-       if (flags & MPOL_F_NUMA_BALANCING) {
-               if (new && new->mode == MPOL_BIND) {
-                       new->flags |= (MPOL_F_MOF | MPOL_F_MORON);
-               } else {
-                       ret = -EINVAL;
-                       mpol_put(new);
-                       goto out;
-               }
-       }
-
        ret = mpol_set_nodemask(new, nodes, scratch);
        if (ret) {
                mpol_put(new);
@@ -1458,7 +1448,11 @@ static inline int sanitize_mpol_flags(int *mode, unsigned short *flags)
                return -EINVAL;
        if ((*flags & MPOL_F_STATIC_NODES) && (*flags & MPOL_F_RELATIVE_NODES))
                return -EINVAL;
-
+       if (*flags & MPOL_F_NUMA_BALANCING) {
+               if (*mode != MPOL_BIND)
+                       return -EINVAL;
+               *flags |= (MPOL_F_MOF | MPOL_F_MORON);
+       }
        return 0;
 }