Re: [syzbot] riscv/fixes boot error: BUG: unable to handle kernel NULL pointer dereference in corrupted

[Vlastimil Babka <vbabka@suse.cz>]

On 9/14/21 12:55, Tetsuo Handa wrote:
> Hmm, I feel that something is wrong with slub... Any idea?

Weird.

> #syz dup: BUG: unable to handle kernel paging request in tomoyo_encode2
> 
> On 2021/09/14 19:39, syzbot wrote:
>> Hello,
>> 
>> syzbot found the following issue on:
>> 
>> HEAD commit:    7d2a07b76933 Linux 5.14
>> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb131b300000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=f8211b06020972e8
>> dashboard link: https://syzkaller.appspot.com/bug?extid=2a1797e8845b57b4a3c2
>> compiler:       riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
>> userspace arch: riscv64
>> 
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+2a1797e8845b57b4a3c2@syzkaller.appspotmail.com
>> 
>> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000d48
>> Oops [#1]
>> Modules linked in:
>> CPU: 1 PID: 2924 Comm: kworker/u4:5 Not tainted 5.14.0-syzkaller #0
>> Hardware name: riscv-virtio,qemu (DT)
>> epc : slab_alloc_node mm/slub.c:2900 [inline]

That's this line:

tid = this_cpu_read(s->cpu_slab->tid);

This would mean something's off with the percpu variable s->cpu_slab.

Looking at the original report:
https://lore.kernel.org/all/000000000000bae2cf05cad87aff@google.com/

That's even more weird, we passed this line but crashed a bit later in
this_cpu_cmpxchg_double() which also accesses s->cpu_slab. Did the "s"
pointer itself get corrupted?

>> epc : slab_alloc mm/slub.c:2967 [inline]
>> epc : __kmalloc+0xce/0x388 mm/slub.c:4111
>>  ra : slab_pre_alloc_hook mm/slab.h:494 [inline]
>>  ra : slab_alloc_node mm/slub.c:2880 [inline]
>>  ra : slab_alloc mm/slub.c:2967 [inline]
>>  ra : __kmalloc+0x6e/0x388 mm/slub.c:4111
>> epc : ffffffff803e3568 ra : ffffffff803e3508 sp : ffffffe008c6f780
>>  gp : ffffffff83f967d8 tp : ffffffe00b71df00 t0 : ffffffc400b37600
>>  t1 : 0000000000000001 t2 : 0000000000000000 s0 : ffffffe008c6f820
>>  s1 : ffffffe005601500 a0 : 0000000000000000 a1 : ffffffe008c6fb6c
>>  a2 : 1ffffffc016e3d07 a3 : 0000000000000d48 a4 : 0000000000000001
>>  a5 : ffffffff82e4b290 a6 : 0000000000f00000 a7 : ffffffff8038ca52
>>  s2 : ffffffff83f96adc s3 : 0000000000000d40 s4 : 0000000000000019
>>  s5 : ffffffff8080a860 s6 : ffffffff83f9a0d0 s7 : 0000000000000000
>>  s8 : 0000000000000d40 s9 : 0000000000000001 s10: ffffffe005aeb6e0
>>  s11: 000000000000002f t3 : 4f89673883b77f00 t4 : ffffffc40118df07
>>  t5 : ffffffc40118df09 t6 : ffffffe0059baffe
>> status: 0000000000000120 badaddr: 0000000000000d48 cause: 000000000000000d
>> [<ffffffff803e3568>] slab_alloc_node mm/slub.c:2900 [inline]
>> [<ffffffff803e3568>] slab_alloc mm/slub.c:2967 [inline]
>> [<ffffffff803e3568>] __kmalloc+0xce/0x388 mm/slub.c:4111
>> [<ffffffff8080a860>] kmalloc include/linux/slab.h:596 [inline]
>> [<ffffffff8080a860>] kzalloc include/linux/slab.h:721 [inline]
>> [<ffffffff8080a860>] tomoyo_encode2.part.0+0xf0/0x262 security/tomoyo/realpath.c:45
>> [<ffffffff8080abc2>] tomoyo_encode2 security/tomoyo/realpath.c:31 [inline]
>> [<ffffffff8080abc2>] tomoyo_encode security/tomoyo/realpath.c:80 [inline]
>> [<ffffffff8080abc2>] tomoyo_realpath_from_path+0x14c/0x3f4 security/tomoyo/realpath.c:288
>> [<ffffffff807f17e8>] tomoyo_init_log+0x7a2/0x13aa security/tomoyo/audit.c:263
>> [<ffffffff807f9c1e>] tomoyo_supervisor+0x1bc/0xb0c security/tomoyo/common.c:2097
>> [<ffffffff80801ca0>] tomoyo_audit_env_log security/tomoyo/environ.c:36 [inline]
>> [<ffffffff80801ca0>] tomoyo_env_perm+0x100/0x120 security/tomoyo/environ.c:63
>> [<ffffffff80801798>] tomoyo_environ security/tomoyo/domain.c:672 [inline]
>> [<ffffffff80801798>] tomoyo_find_next_domain+0xd24/0x109a security/tomoyo/domain.c:879
>> [<ffffffff8080c098>] tomoyo_bprm_check_security security/tomoyo/tomoyo.c:101 [inline]
>> [<ffffffff8080c098>] tomoyo_bprm_check_security+0xdc/0x136 security/tomoyo/tomoyo.c:91
>> [<ffffffff807e8b8e>] security_bprm_check+0x44/0x96 security/security.c:866
>> [<ffffffff80438242>] search_binary_handler fs/exec.c:1709 [inline]
>> [<ffffffff80438242>] exec_binprm fs/exec.c:1762 [inline]
>> [<ffffffff80438242>] bprm_execve fs/exec.c:1831 [inline]
>> [<ffffffff80438242>] bprm_execve+0x4ba/0x10a6 fs/exec.c:1793
>> [<ffffffff80439e7c>] kernel_execve+0x204/0x288 fs/exec.c:1974
>> [<ffffffff8005afec>] call_usermodehelper_exec_async+0x1bc/0x2d8 kernel/umh.c:112
>> [<ffffffff8000515e>] ret_from_exception+0x0/0x14
>> ---[ end trace 77235688c0a8656b ]---
>> 
>> 
>> ---
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>> 
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>> 
> 
>