Re: [External] Re: [PATCH] mm/ksm: Fix kernel NULL pointer dereference at 0000000000000040

[Muchun Song]

On Tue, Apr 14, 2020 at 8:23 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 14.04.20 14:09, Muchun Song wrote:
> > On Tue, Apr 14, 2020 at 7:48 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
> >>
> >> On 14.04.20 08:20, Muchun Song wrote:
> >>> The find_mergeable_vma can return NULL. In this case, it leads
> >>> to crash when we access vma->vm_mm(which's offset is 0x40) in
> >>> write_protect_page. And this case did happen on our server. The
> >>> following calltrace is captured in kernel 4.19 with ksm enabled.
> >>> So add a vma check to fix it.
> >>>
> >>> --------------------------------------------------------------------------
> >>>   BUG: unable to handle kernel NULL pointer dereference at 0000000000000040
> >>>   PGD 0 P4D 0
> >>>   Oops: 0000 [#1] SMP NOPTI
> >>>   CPU: 9 PID: 510 Comm: ksmd Kdump: loaded Tainted: G OE 4.19.36.bsk.9-amd64 #4.19.36.bsk.9
> >>>   Hardware name: FOXCONN R-5111/GROOT, BIOS IC1B111F 08/17/2019
> >>>   RIP: 0010:try_to_merge_one_page+0xc7/0x760
> >>>   Code: 24 58 65 48 33 34 25 28 00 00 00 89 e8 0f 85 a3 06 00 00 48 83 c4
> >>>         60 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 46 08 a8 01 75 b8 <49>
> >>>         8b 44 24 40 4c 8d 7c 24 20 b9 07 00 00 00 4c 89 e6 4c 89 ff 48
> >>>   RSP: 0018:ffffadbdd9fffdb0 EFLAGS: 00010246
> >>>   RAX: ffffda83ffd4be08 RBX: ffffda83ffd4be40 RCX: 0000002c6e800000
> >>>   RDX: 0000000000000000 RSI: ffffda83ffd4be40 RDI: 0000000000000000
> >>>   RBP: ffffa11939f02ec0 R08: 0000000094e1a447 R09: 00000000abe76577
> >>>   R10: 0000000000000962 R11: 0000000000004e6a R12: 0000000000000000
> >>>   R13: ffffda83b1e06380 R14: ffffa18f31f072c0 R15: ffffda83ffd4be40
> >>>   FS: 0000000000000000(0000) GS:ffffa0da43b80000(0000) knlGS:0000000000000000
> >>>   CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >>>   CR2: 0000000000000040 CR3: 0000002c77c0a003 CR4: 00000000007626e0
> >>>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >>>   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >>>   PKRU: 55555554
> >>>   Call Trace:
> >>>     ? follow_page_pte+0x36d/0x5e0
> >>>     ksm_scan_thread+0x115e/0x1960
> >>>     ? remove_wait_queue+0x60/0x60
> >>>     kthread+0xf5/0x130
> >>>     ? try_to_merge_with_ksm_page+0x90/0x90
> >>>     ? kthread_create_worker_on_cpu+0x70/0x70
> >>>     ret_from_fork+0x1f/0x30
> >>> --------------------------------------------------------------------------
> >>>
> >>> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> >>> Signed-off-by: Xiongchun duan <duanxiongchun@xxxxxxxxxxxxx>
> >>
> >> ^ why this signed-off ?
> >>
> >
> > Because I have a partner. And I just sent the v2 patch which updates the
> > commit message and patch subject. Thanks for your review.
>
> Then we use Co-developed-by AFAIK instead.
>

Thanks a lot. I will fix it.

-- 
Yours,
Muchun