linux-kernel - Re: [Syzkaller & bisect] There is BUG: unable to handle kernel paging request in fuse_copy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <77ace07b-3f84-46ac-8a29-e782d7f60078@redhat.com>
Date: Wed, 31 Jan 2024 11:54:25 +0100
From: David Hildenbrand <david@...hat.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Pengfei Xu <pengfei.xu@...el.com>, rdunlap@...radead.org,
 akpm@...ux-foundation.org, heng.su@...el.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, lkp@...el.com
Subject: Re: [Syzkaller & bisect] There is BUG: unable to handle kernel paging
 request in fuse_copy_one in intel-6.8-rc2

On 31.01.24 11:48, Mike Rapoport wrote:
> On Wed, Jan 31, 2024 at 10:15:11AM +0100, David Hildenbrand wrote:
>> On 31.01.24 03:01, Pengfei Xu wrote:
>>> Hi Mike,
>>>
>>> Greeting!
>>>
>>> There is "unable to handle kernel paging request in fuse_copy_one" BUG in
>>> intel-6.8-rc2:
>>>
>>> All detailed info: https://github.com/xupengfe/syzkaller_logs/tree/main/240130_184751_fuse_copy_one
>>> Syzkaller reproduced code: https://github.com/xupengfe/syzkaller_logs/blob/main/240130_184751_fuse_copy_one/repro.c
>>> Syzkaller repro syscall steps: https://github.com/xupengfe/syzkaller_logs/blob/main/240130_184751_fuse_copy_one/repro.prog
>>> Bisect info: https://github.com/xupengfe/syzkaller_logs/blob/main/240130_184751_fuse_copy_one/bisect_info.log
>>> Issue dmesg: https://github.com/xupengfe/syzkaller_logs/blob/main/240130_184751_fuse_copy_one/41bccc98fb7931d63d03f326a746ac4d429c1dd3_dmesg.log
>>> bzImage: https://github.com/xupengfe/syzkaller_logs/raw/main/240130_184751_fuse_copy_one/bzImage_v6.8-rc2.tar.gz
>>> Kconfig(make olddefconfig): https://github.com/xupengfe/syzkaller_logs/blob/main/240130_184751_fuse_copy_one/kconfig_origin
>>>
>>> Bisected and found first bad commit is:
>>> b758fe6df50da mm/secretmem: make it on by default
>>
>> Sounds like we manage to access a page that has its direct map removed --
>> either because it's actual secretmem memory, or because we fail to restore
>> the direct map.
> 
> Judging by the repro code and the registers, it's an access to secretmem.
> 
> The call
> syscall(__NR_write, /*fd=*/r[0], /*arg=*/0x20000040ul, /*len=*/0x50ul);
> 
> will eventually get to
> 
> memcpy(0xffff88800e2afa80, 0xffff8880119a5040, 0x0000000000000010)
> 
> and I think that 0x20000040 in repro address space maps to
> 0xffff8880119a5040 in the direct map.
> 
> So it looks like secretmem actually works :)

Good. How can we prevent triggering BUGs? The write system call should 
fail gracefully (and I thought it would).

-- 
Cheers,

David / dhildenb