Re: [PATCH] mm/mempolicy: do not allow illegal MPOL_F_NUMA_BALANCING | MPOL_LOCAL in mbind()

[Dongliang Mu]

On Sat, Oct 2, 2021 at 1:49 AM Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>
> From: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> 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
> RIP: 0033:0x7f4a41b2c709
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f4a3f0a3188 EFLAGS: 00000246 ORIG_RAX: 00000000000000ed
> RAX: ffffffffffffffda RBX: 00007f4a41c30f60 RCX: 00007f4a41b2c709
> RDX: 0000000000002001 RSI: 0000000000c00007 RDI: 0000000020012000
> RBP: 00007f4a41b86cb4 R08: 0000000000000000 R09: 0000010000000002
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f4a42164b2f R14: 00007f4a3f0a3300 R15: 0000000000022000
>

Hi Eric,

this crash seems like the bug report [1] on Syzbot dashboard.

[1] https://syzkaller.appspot.com/bug?id=028833194204bb15c2c43d822b8f7401360d57f5

If yes, maybe you can push a patch testing request.

> Fixes: bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes")
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
> Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> ---
>  mm/mempolicy.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 1592b081c58ef6dd63c6f075ad24722f2be7cb5d..7a7abdbec7af66f88bb68cb4f47e9722d56bfd5b 100644
> --- 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;
>  }
>
> --
> 2.33.0.800.g4c38ced690-goog
>
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