linux-kernel - Re: [syzbot] [jfs?] UBSAN: shift-out-of-bounds in extAlloc (2)

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Message-ID: <68d8a871.a00a0220.102ee.0024.GAE@google.com>
Date: Sat, 27 Sep 2025 20:16:01 -0700
From: syzbot <syzbot+13e8cd4926977f8337b6@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	xandfury@...il.com
Subject: Re: [syzbot] [jfs?] UBSAN: shift-out-of-bounds in extAlloc (2)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
UBSAN: shift-out-of-bounds in extAlloc

loop0: detected capacity change from 0 to 32768
------------[ cut here ]------------
UBSAN: shift-out-of-bounds in fs/jfs/jfs_extent.c:329:16
shift exponent 64 is too large for 64-bit type 's64' (aka 'long long')
CPU: 0 UID: 0 PID: 6607 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 ubsan_epilogue+0xa/0x40 lib/ubsan.c:233
 __ubsan_handle_shift_out_of_bounds+0x386/0x410 lib/ubsan.c:494
 extBalloc fs/jfs/jfs_extent.c:329 [inline]
 extAlloc+0xd52/0xfb0 fs/jfs/jfs_extent.c:127
 jfs_get_block+0x346/0xab0 fs/jfs/inode.c:248
 __block_write_begin_int+0x6b2/0x1900 fs/buffer.c:2145
 block_write_begin+0x8a/0x120 fs/buffer.c:2256
 jfs_write_begin+0x35/0x80 fs/jfs/inode.c:300
 generic_perform_write+0x29a/0x8c0 mm/filemap.c:4175
 generic_file_write_iter+0x118/0x550 mm/filemap.c:4318
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5d2/0xb40 fs/read_write.c:686
 ksys_write+0x14b/0x260 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fddbbcbebe9
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:00007fddbb32e038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fddbbee5fa0 RCX: 00007fddbbcbebe9
RDX: 00000000fffffdef RSI: 00002000000000c0 RDI: 0000000000000005
RBP: 00007fddbbd41e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fddbbee6038 R14: 00007fddbbee5fa0 R15: 00007ffefffbcc18
 </TASK>
---[ end trace ]---


Tested on:

commit:         51a24b7d Merge tag 'trace-tools-v6.17-rc5' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15f67142580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f5b21423ca3f0a96
dashboard link: https://syzkaller.appspot.com/bug?extid=13e8cd4926977f8337b6
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Note: no patches were applied.