[syzbot] general protection fault in fuse_test_super

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: aa14a3016182 Add linux-next specific files for 20210910
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=148da295300000
kernel config: https://syzkaller.appspot.com/x/.config?x=e400f2d70a0ed309
dashboard link: https://syzkaller.appspot.com/bug?extid=74a15f02ccb51f398601
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12da37b9300000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10bb87ed300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+74a15f...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 PID: 6638 Comm: syz-executor038 Not tainted 5.14.0-next-20210910-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:get_fuse_conn_super fs/fuse/fuse_i.h:844 [inline]
RIP: 0010:fuse_test_super+0x68/0xa0 fs/fuse/inode.c:1633
Code: 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 75 3a 48 8b 9b 78 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 <80> 3c 02 00 75 12 31 c0 48 39 2b 5b 5d 0f 94 c0 c3 e8 92 9f 0d ff
RSP: 0018:ffffc90002e1fcc8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff82ae91fd RDI: ffff8880750a4678
RBP: ffff88801ca4d000 R08: 0000000000000001 R09: 0000000000000003
R10: fffff520005c3f8e R11: 0000000000000000 R12: dffffc0000000000
R13: ffffffff82ae91f0 R14: 0000000000000000 R15: 0000000000000002
FS: 0000000000fd5300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd112d1758 CR3: 0000000071247000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
sget_fc+0x1ff/0x7c0 fs/super.c:525
fuse_get_tree+0x201/0x3f0 fs/fuse/inode.c:1664
vfs_get_tree+0x89/0x2f0 fs/super.c:1498
do_new_mount fs/namespace.c:2988 [inline]
path_mount+0x1320/0x1fa0 fs/namespace.c:3318
do_mount fs/namespace.c:3331 [inline]
__do_sys_mount fs/namespace.c:3539 [inline]
__se_sys_mount fs/namespace.c:3516 [inline]
__x64_sys_mount+0x27f/0x300 fs/namespace.c:3516
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+0x44/0xae
RIP: 0033:0x440089
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 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:00007ffd112d1778 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000483088 RCX: 0000000000440089
RDX: 0000000020002100 RSI: 00000000200020c0 RDI: 0000000000000000
RBP: 0030656c69662f2e R08: 00000000200004c0 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000010bf1
R13: 00007ffd112d178c R14: 00007ffd112d17a0 R15: 00007ffd112d1790
Modules linked in:
---[ end trace 750f18e3bec431c4 ]---
RIP: 0010:get_fuse_conn_super fs/fuse/fuse_i.h:844 [inline]
RIP: 0010:fuse_test_super+0x68/0xa0 fs/fuse/inode.c:1633
Code: 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 75 3a 48 8b 9b 78 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 <80> 3c 02 00 75 12 31 c0 48 39 2b 5b 5d 0f 94 c0 c3 e8 92 9f 0d ff
RSP: 0018:ffffc90002e1fcc8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff82ae91fd RDI: ffff8880750a4678
RBP: ffff88801ca4d000 R08: 0000000000000001 R09: 0000000000000003
R10: fffff520005c3f8e R11: 0000000000000000 R12: dffffc0000000000
R13: ffffffff82ae91f0 R14: 0000000000000000 R15: 0000000000000002
FS: 0000000000fd5300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd112d1758 CR3: 0000000071247000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess), 4 bytes skipped:
0: df 48 89 fisttps -0x77(%rax)
3: fa cli
4: 48 c1 ea 03 shr $0x3,%rdx
8: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1)
c: 75 3a jne 0x48
e: 48 8b 9b 78 06 00 00 mov 0x678(%rbx),%rbx
15: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
1c: fc ff df
1f: 48 89 da mov %rbx,%rdx
22: 48 c1 ea 03 shr $0x3,%rdx
* 26: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction
2a: 75 12 jne 0x3e
2c: 31 c0 xor %eax,%eax
2e: 48 39 2b cmp %rbp,(%rbx)
31: 5b pop %rbx
32: 5d pop %rbp
33: 0f 94 c0 sete %al
36: c3 retq
37: e8 92 9f 0d ff callq 0xff0d9fce


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Miklos Szeredi]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git
80019f1138324b6f35ae728b4f25eeb08899b452

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+74a15f...@syzkaller.appspotmail.com

Tested on:

commit: 80019f11 fuse: always initialize sb->s_fs_info
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git
kernel config: https://syzkaller.appspot.com/x/.config?x=3decadb8235b4dad
dashboard link: https://syzkaller.appspot.com/bug?extid=74a15f02ccb51f398601
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Note: testing is done by a robot and is best-effort only.