[Android 5.10] BUG: unable to handle kernel NULL pointer dereference in z_erofs_decompress

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e253c52bbdfc Merge 5.10.247 into android13-5.10-lts
git tree: android13-5.10-lts
console output: https://syzkaller.appspot.com/x/log.txt?x=10bf7c9a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=5193c33e6e6dcf8b
dashboard link: https://syzkaller.appspot.com/bug?extid=4de80acc7c04fedb64e9
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16ff7cfc580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11ed3bb4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1f48e3a38826/disk-e253c52b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/17f909517783/vmlinux-e253c52b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1fc1230e0a59/bzImage-e253c52b.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/a427bf167a11/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=12b6349a580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4de80a...@syzkaller.appspotmail.com

erofs: (device loop2): mounted with root inode @ nid 36.
erofs: (device loop2): z_erofs_extent_lookback: bogus lookback distance @ nid 36
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 10ffb6067 P4D 10ffb6067 PUD 0
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 367 Comm: syz.2.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc90000da6bc8 EFLAGS: 00010246
RAX: 1ffffffff0a3b5ce RBX: ffffc90000da7520 RCX: ffff8881101a13c0
RDX: 0000000000000000 RSI: ffffc90000da7520 RDI: ffffc90000da7080
RBP: ffffc90000da6bf0 R08: dffffc0000000000 R09: ffffc90000da70aa
R10: fffff520001b4e16 R11: 1ffff920001b4e15 R12: dffffc0000000000
R13: 000000000000073b R14: ffffc90000da7080 R15: ffffffff851dae70
FS: 000055555db6a500(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000010b9d8000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
z_erofs_decompress+0x79/0xb0 fs/erofs/decompressor.c:360
z_erofs_decompress_pcluster fs/erofs/zdata.c:1110 [inline]
z_erofs_decompress_queue+0x1066/0x1a10 fs/erofs/zdata.c:1188
z_erofs_runqueue+0x11c9/0x1230 fs/erofs/zdata.c:1515
z_erofs_readpage+0x1f3/0x480 fs/erofs/zdata.c:1533
do_read_cache_page+0x69b/0xaa0 mm/filemap.c:-1
read_cache_page+0x50/0x70 mm/filemap.c:3296
read_mapping_page include/linux/pagemap.h:498 [inline]
find_target_block_classic fs/erofs/namei.c:104 [inline]
erofs_namei+0x162/0x10d0 fs/erofs/namei.c:184
erofs_lookup+0xa5/0x260 fs/erofs/namei.c:228
__lookup_slow+0x2aa/0x3e0 fs/namei.c:1648
lookup_slow+0x57/0x70 fs/namei.c:1665
walk_component+0x325/0x460 fs/namei.c:1960
link_path_walk+0x5b2/0xb80 fs/namei.c:-1
path_openat+0x27c/0x3160 fs/namei.c:3513
do_filp_open+0x1b3/0x3e0 fs/namei.c:3544
do_sys_openat2+0x14c/0x6d0 fs/open.c:1219
do_sys_open fs/open.c:1235 [inline]
__do_sys_open fs/open.c:1243 [inline]
__se_sys_open fs/open.c:1239 [inline]
__x64_sys_open+0x11c/0x140 fs/open.c:1239
do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f4768bac749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc55344648 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007f4768e02fa0 RCX: 00007f4768bac749
RDX: 0000000000000000 RSI: 00000000001a1342 RDI: 0000200000000000
RBP: 00007f4768c30f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4768e02fa0 R14: 00007f4768e02fa0 R15: 0000000000000003
Modules linked in:
CR2: 0000000000000000
---[ end trace b09bedc3b357de73 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc90000da6bc8 EFLAGS: 00010246
RAX: 1ffffffff0a3b5ce RBX: ffffc90000da7520 RCX: ffff8881101a13c0
RDX: 0000000000000000 RSI: ffffc90000da7520 RDI: ffffc90000da7080
RBP: ffffc90000da6bf0 R08: dffffc0000000000 R09: ffffc90000da70aa
R10: fffff520001b4e16 R11: 1ffff920001b4e15 R12: dffffc0000000000
R13: 000000000000073b R14: ffffc90000da7080 R15: ffffffff851dae70
FS: 000055555db6a500(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000010b9d8000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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