[syzbot] general protection fault in btrfs_ioctl_send

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    9e46a7996732 Add linux-next specific files for 20221125
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1518a973880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=11e19c740a0b2926
dashboard link: https://syzkaller.appspot.com/bug?extid=c423003741c992ccf56b
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=1024ec05880000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12bc0973880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/758d818cf966/disk-9e46a799.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f7c8696b40a5/vmlinux-9e46a799.xz
kernel image: https://storage.googleapis.com/syzbot-assets/810f9750b87f/bzImage-9e46a799.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/9b34ff4df466/mount_0.gz

The issue was bisected to:

commit d14cd51f13589142902687cfacd09e373251ac6e
Author: Filipe Manana <fdmanana@xxxxxxxx>
Date:   Tue Nov 1 16:15:50 2022 +0000

    btrfs: send: cache leaf to roots mapping during backref walking

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17d92353880000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=14392353880000
console output: https://syzkaller.appspot.com/x/log.txt?x=10392353880000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c423003741c992ccf56b@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: d14cd51f1358 ("btrfs: send: cache leaf to roots mapping during backref walking")

BTRFS info (device loop0): enabling ssd optimizations
BTRFS info (device loop0): auto enabling async discard
BTRFS info (device loop0): checking UUID tree
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: 5294 Comm: syz-executor236 Not tainted 6.1.0-rc6-next-20221125-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
RIP: 0010:empty_backref_cache fs/btrfs/send.c:1396 [inline]
RIP: 0010:btrfs_ioctl_send+0x13ab/0x65a0 fs/btrfs/send.c:8365
Code: 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 49 1c 00 00 4d 8b ae c0 01 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 <80> 3c 02 00 0f 85 34 1c 00 00 4c 39 ed 49 8b 5d 00 49 bc 00 00 00
RSP: 0018:ffffc90003bbf8c8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff88807735f140 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8380b588 RDI: ffff88807735f000
RBP: ffff88807735f1c0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffed100ee6be28
R13: 0000000000000000 R14: ffff88807735f000 R15: 0000000000000000
FS:  00005555556b3300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff4af8bff8 CR3: 000000007dbc9000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 _btrfs_ioctl_send+0x231/0x2e0 fs/btrfs/ioctl.c:4343
 btrfs_ioctl+0x4058/0x5870 fs/btrfs/ioctl.c:4634
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x197/0x210 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f5d8166ab09
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 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:00007fff55cc13f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5d8166ab09
RDX: 0000000020000040 RSI: 0000000040489426 RDI: 0000000000000003
RBP: 00007f5d8162a3d0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5d8162a460
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:empty_backref_cache fs/btrfs/send.c:1396 [inline]
RIP: 0010:btrfs_ioctl_send+0x13ab/0x65a0 fs/btrfs/send.c:8365
Code: 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 49 1c 00 00 4d 8b ae c0 01 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 <80> 3c 02 00 0f 85 34 1c 00 00 4c 39 ed 49 8b 5d 00 49 bc 00 00 00
RSP: 0018:ffffc90003bbf8c8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff88807735f140 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8380b588 RDI: ffff88807735f000
RBP: ffff88807735f1c0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffed100ee6be28
R13: 0000000000000000 R14: ffff88807735f000 R15: 0000000000000000
FS:  00005555556b3300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff4af8bff8 CR3: 000000007dbc9000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess), 4 bytes skipped:
   0:	48 c1 ea 03          	shr    $0x3,%rdx
   4:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
   8:	0f 85 49 1c 00 00    	jne    0x1c57
   e:	4d 8b ae c0 01 00 00 	mov    0x1c0(%r14),%r13
  15:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  1c:	fc ff df
  1f:	4c 89 ea             	mov    %r13,%rdx
  22:	48 c1 ea 03          	shr    $0x3,%rdx
* 26:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2a:	0f 85 34 1c 00 00    	jne    0x1c64
  30:	4c 39 ed             	cmp    %r13,%rbp
  33:	49 8b 5d 00          	mov    0x0(%r13),%rbx
  37:	49                   	rex.WB
  38:	bc                   	.byte 0xbc
  39:	00 00                	add    %al,(%rax)


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