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

[Eric Dumazet <edumazet@google.com>]

On Thu, Oct 7, 2021 at 10:26 PM Dongliang Mu <mudongliangabcd@gmail.com> wrote:
>
> On Sat, Oct 2, 2021 at 1:49 AM Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >
> > From: Eric Dumazet <edumazet@google.com>
> >
> > 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.
>

No, it was a different syzbot report, currently held in our queue.

(Andrew Morton has access to our internal bug, I CC him (b/201266830))

I can release it, at the expense of more noise to various mailing
lists, but really the bug is trivial.