[syzbot] general protection fault in exfat_fill_super

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4d48f589d294 Add linux-next specific files for 20221021
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=11fc516e880000
kernel config: https://syzkaller.appspot.com/x/.config?x=2c4b7d600a5739a6
dashboard link: https://syzkaller.appspot.com/bug?extid=74fa8cb75d0a18df4790
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1056a9b4880000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14613b3c880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0c86bd0b39a0/disk-4d48f589.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/074059d37f1f/vmlinux-4d48f589.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/6d392b37ac66/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+74fa8c...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 4096
general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 PID: 3610 Comm: syz-executor183 Not tainted 6.1.0-rc1-next-20221021-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
RIP: 0010:strcmp+0x35/0xb0 lib/string.c:281
Code: df 41 54 55 53 48 89 fb 48 83 ec 08 eb 08 40 84 ed 74 5d 4c 89 e6 48 89 df 48 83 c3 01 48 89 f8 48 89 fa 48 c1 e8 03 83 e2 07 <42> 0f b6 04 28 38 d0 7f 04 84 c0 75 50 0f b6 6b ff 4c 8d 66 01 48
RSP: 0018:ffffc90003e3fbd8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff89e65300 RDI: 0000000000000000
RBP: ffffc90003e3fd38 R08: 0000000000000005 R09: 0000000000000100
R10: 0000000000000100 R11: 1ffffffff17b2629 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff8880766a6000 R15: 0000000000000100
FS: 0000555556f6b300(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005d84c8 CR3: 0000000072c9f000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
exfat_fill_super+0x16d0/0x2990 fs/exfat/super.c:659
get_tree_bdev+0x440/0x760 fs/super.c:1324
vfs_get_tree+0x89/0x2f0 fs/super.c:1531
do_new_mount fs/namespace.c:3040 [inline]
path_mount+0x1326/0x1e20 fs/namespace.c:3370
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount fs/namespace.c:3568 [inline]
__x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fa8d401085a
Code: 83 c4 08 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdbcd10b08 EFLAGS: 00000286 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fa8d401085a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007ffdbcd10b20
RBP: 00007ffdbcd10b20 R08: 00007ffdbcd10b60 R09: 0000555556f6b2c0
R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000000004
R13: 00007ffdbcd10b60 R14: 000000000000001d R15: 00000000200004b8
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:strcmp+0x35/0xb0 lib/string.c:281
Code: df 41 54 55 53 48 89 fb 48 83 ec 08 eb 08 40 84 ed 74 5d 4c 89 e6 48 89 df 48 83 c3 01 48 89 f8 48 89 fa 48 c1 e8 03 83 e2 07 <42> 0f b6 04 28 38 d0 7f 04 84 c0 75 50 0f b6 6b ff 4c 8d 66 01 48
RSP: 0018:ffffc90003e3fbd8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff89e65300 RDI: 0000000000000000
RBP: ffffc90003e3fd38 R08: 0000000000000005 R09: 0000000000000100
R10: 0000000000000100 R11: 1ffffffff17b2629 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff8880766a6000 R15: 0000000000000100
FS: 0000555556f6b300(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005d84c8 CR3: 0000000072c9f000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: df 41 54 filds 0x54(%rcx)
3: 55 push %rbp
4: 53 push %rbx
5: 48 89 fb mov %rdi,%rbx
8: 48 83 ec 08 sub $0x8,%rsp
c: eb 08 jmp 0x16
e: 40 84 ed test %bpl,%bpl
11: 74 5d je 0x70
13: 4c 89 e6 mov %r12,%rsi
16: 48 89 df mov %rbx,%rdi
19: 48 83 c3 01 add $0x1,%rbx
1d: 48 89 f8 mov %rdi,%rax
20: 48 89 fa mov %rdi,%rdx
23: 48 c1 e8 03 shr $0x3,%rax
27: 83 e2 07 and $0x7,%edx
* 2a: 42 0f b6 04 28 movzbl (%rax,%r13,1),%eax <-- trapping instruction
2f: 38 d0 cmp %dl,%al
31: 7f 04 jg 0x37
33: 84 c0 test %al,%al
35: 75 50 jne 0x87
37: 0f b6 6b ff movzbl -0x1(%rbx),%ebp
3b: 4c 8d 66 01 lea 0x1(%rsi),%r12
3f: 48 rex.W


---
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[Namjae Jeon]

Hello,

I have tried to reproduce this issue using syzkaller and your
testcase(C reproducer)

root@syzkaller:~# ./repro
[ 4278.566005] loop0: detected capacity change from 0 to 4096
[ 4278.570538] exfat: Bad value for 'iocharset

But I can't see kernel oops or KASAN logs.
Could you pleaes confirm that you can still reproduce this ?

Thanks!

2022-10-24 18:56 GMT+09:00, syzbot
<syzbot+74fa8c...@syzkaller.appspotmail.com>:

[Dmitry Vyukov]

On Wed, 30 Nov 2022 at 16:17, Namjae Jeon <linki...@kernel.org> wrote:
>
> Hello,
>
> I have tried to reproduce this issue using syzkaller and your
> testcase(C reproducer)
>
> root@syzkaller:~# ./repro
> [ 4278.566005] loop0: detected capacity change from 0 to 4096
> [ 4278.570538] exfat: Bad value for 'iocharset
>
> But I can't see kernel oops or KASAN logs.
> Could you pleaes confirm that you can still reproduce this ?

Hi Namjae,

This was reported by a robot, it won't understand such a request.
But you can see all the info it has about the bug on the dashboard
page (when it happened, how many times, on what commits, etc):
https://syzkaller.appspot.com/bug?extid=74fa8cb75d0a18df4790

I am assuming you used the provided kernel commit and config. If you
can't reproduce it, but need it for debugging/testing, you can ask
syzbot to test your patches.

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[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.