[syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in __bch2_bkey_unpack_key

[syzbot <syzbot+cfd994b9cdf00446fd54@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    785cdec46e92 Merge tag 'x86-core-2025-05-25' of git://git...
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=10b5adf4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cf9956a5a76267c7
dashboard link: https://syzkaller.appspot.com/bug?extid=cfd994b9cdf00446fd54
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11e626d4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15e626d4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0672bd8fdf4a/disk-785cdec4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/df460fea958f/vmlinux-785cdec4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7ae41e61549e/bzImage-785cdec4.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/8a6de6365ccd/mount_0.gz

The issue was bisected to:

commit cd3cdb1ef706a1ac725194d81858d58375739b25
Author: Kent Overstreet <kent.overstreet@linux.dev>
Date:   Tue Apr 22 13:14:19 2025 +0000

    bcachefs: Single err message for btree node reads

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=138c6df4580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=104c6df4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=178c6df4580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cfd994b9cdf00446fd54@syzkaller.appspotmail.com
Fixes: cd3cdb1ef706 ("bcachefs: Single err message for btree node reads")

bcachefs (loop0): sb invalid before write: Unsupported superblock version_min 0.0: (unknown version) (min 0.9: (unknown version), max 1.28: inode_has_case_insensitive)
  emergency read only at seq 10
------------[ cut here ]------------
UBSAN: shift-out-of-bounds in fs/bcachefs/bkey.c:163:16
shift exponent 4294967127 is too large for 64-bit type 'u64' (aka 'unsigned long long')
CPU: 0 UID: 0 PID: 5832 Comm: read_btree_node Not tainted 6.15.0-syzkaller-01958-g785cdec46e92 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 ubsan_epilogue+0xa/0x40 lib/ubsan.c:231
 __ubsan_handle_shift_out_of_bounds+0x386/0x410 lib/ubsan.c:492
 get_inc_field fs/bcachefs/bkey.c:163 [inline]
 __bch2_bkey_unpack_key+0xdc4/0xe10 fs/bcachefs/bkey.c:284
 __bch2_bkey_compat+0x4db/0xbd0 fs/bcachefs/bkey_methods.c:480
 bch2_bkey_compat fs/bcachefs/bkey_methods.h:134 [inline]
 validate_bset_keys+0x6c1/0x1390 fs/bcachefs/btree_io.c:983
 bch2_btree_node_read_done+0x18c8/0x4f60 fs/bcachefs/btree_io.c:1211
 btree_node_read_work+0x426/0xe30 fs/bcachefs/btree_io.c:1400
 bch2_btree_node_read+0x887/0x29f0 fs/bcachefs/btree_io.c:-1
 bch2_btree_node_fill+0xd12/0x14f0 fs/bcachefs/btree_cache.c:994
 bch2_btree_node_get_noiter+0xa2c/0x1000 fs/bcachefs/btree_cache.c:1261
 found_btree_node_is_readable fs/bcachefs/btree_node_scan.c:85 [inline]
 try_read_btree_node fs/bcachefs/btree_node_scan.c:220 [inline]
 read_btree_nodes_worker+0x1319/0x1e20 fs/bcachefs/btree_node_scan.c:269
 kthread+0x711/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x4e/0x80 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
---[ end trace ]---


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