* David Hildenbrand <david@xxxxxxxxxx> [241120 15:12]:
> We currently assume that there is at least one VMA in a MM, which isn't
> true.
>
> So we might end up having find_vma() return NULL, to then de-reference
> NULL. So properly handle find_vma() returning NULL.
>
> This fixes the report:
>
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> CPU: 1 UID: 0 PID: 6021 Comm: syz-executor284 Not tainted 6.12.0-rc7-syzkaller-00187-gf868cd251776 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
> RIP: 0010:migrate_to_node mm/mempolicy.c:1090 [inline]
> RIP: 0010:do_migrate_pages+0x403/0x6f0 mm/mempolicy.c:1194
> Code: ...
> RSP: 0018:ffffc9000375fd08 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffffc9000375fd78 RCX: 0000000000000000
> RDX: ffff88807e171300 RSI: dffffc0000000000 RDI: ffff88803390c044
> RBP: ffff88807e171428 R08: 0000000000000014 R09: fffffbfff2039ef1
> R10: ffffffff901cf78f R11: 0000000000000000 R12: 0000000000000003
> R13: ffffc9000375fe90 R14: ffffc9000375fe98 R15: ffffc9000375fdf8
> FS: 00005555919e1380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005555919e1ca8 CR3: 000000007f12a000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> kernel_migrate_pages+0x5b2/0x750 mm/mempolicy.c:1709
> __do_sys_migrate_pages mm/mempolicy.c:1727 [inline]
> __se_sys_migrate_pages mm/mempolicy.c:1723 [inline]
> __x64_sys_migrate_pages+0x96/0x100 mm/mempolicy.c:1723
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Fixes: 39743889aaf7 ("[PATCH] Swap Migration V5: sys_migrate_pages interface")
> Reported-by: syzbot+3511625422f7aa637f0d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/lkml/673d2696.050a0220.3c9d61.012f.GAE@xxxxxxxxxx/T/
> Cc: <stable@xxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
I hate the extra check because syzbot can cause this as this should
basically never happen in real life, but it seems we have to add it.
I wonder where else this is could show up.
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> mm/mempolicy.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index b646fab3e45e1..fbb6127e4595a 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1080,6 +1080,10 @@ static long migrate_to_node(struct mm_struct *mm, int source, int dest,
>
> mmap_read_lock(mm);
> vma = find_vma(mm, 0);
> + if (!vma) {
> + mmap_read_unlock(mm);
> + return 0;
> + }
>
> /*
> * This does not migrate the range, but isolates all pages that
> --
> 2.47.0
>
>
