Re: [syzbot] UBSAN: shift-out-of-bounds in dbFreeBits

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    4d48f589d294 Add linux-next specific files for 20221021
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=130d1e4a880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2c4b7d600a5739a6
dashboard link: https://syzkaller.appspot.com/bug?extid=cf96cd135c5e00252e3b
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=10dcd48c880000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11a881e2880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0c86bd0b39a0/disk-4d48f589.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/074059d37f1f/vmlinux-4d48f589.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/6ac10f1c36b9/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cf96cd135c5e00252e3b@xxxxxxxxxxxxxxxxxxxxxxxxx

loop0: detected capacity change from 0 to 32768
================================================================================
UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:1681:12
shift exponent -256 is negative
CPU: 1 PID: 3602 Comm: syz-executor318 Not tainted 6.1.0-rc1-next-20221021-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 ubsan_epilogue+0xb/0x50 lib/ubsan.c:151
 __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x187 lib/ubsan.c:322
 dbFreeBits.cold-0x5/0x72
 dbAllocAny+0xa4/0x1a0 fs/jfs/jfs_dmap.c:1512
 dbAlloc+0x46d/0xa70 fs/jfs/jfs_dmap.c:869
 extBalloc fs/jfs/jfs_extent.c:321 [inline]
 extAlloc+0x4e7/0xeb0 fs/jfs/jfs_extent.c:122
 jfs_get_block+0x661/0xa90 fs/jfs/inode.c:248
 __block_write_begin_int+0x3b9/0x14b0 fs/buffer.c:1991
 __block_write_begin fs/buffer.c:2041 [inline]
 block_write_begin+0xb5/0x440 fs/buffer.c:2102
 jfs_write_begin+0x2d/0xd0 fs/jfs/inode.c:304
 generic_perform_write+0x252/0x570 mm/filemap.c:3771
 __generic_file_write_iter+0x2aa/0x4d0 mm/filemap.c:3899
 generic_file_write_iter+0xdf/0x350 mm/filemap.c:3931
 call_write_iter include/linux/fs.h:2191 [inline]
 do_iter_readv_writev+0x20b/0x3b0 fs/read_write.c:735
 do_iter_write+0x182/0x700 fs/read_write.c:861
 vfs_writev+0x1aa/0x630 fs/read_write.c:934
 do_pwritev+0x1b6/0x270 fs/read_write.c:1031
 __do_sys_pwritev2 fs/read_write.c:1090 [inline]
 __se_sys_pwritev2 fs/read_write.c:1081 [inline]
 __x64_sys_pwritev2+0xeb/0x150 fs/read_write.c:1081
 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+0x63/0xcd
RIP: 0033:0x7f93dbe84f69
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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc412c8fb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f93dbe84f69
RDX: 0000000000000002 RSI: 0000000020003380 RDI: 0000000000000003
RBP: 00007f93dbe44730 R08: 0000000002000000 R09: 0000000000000003
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000f8008000
R13: 0000000000000000 R14: 00083878000000fc R15: 0000000000000000
 </TASK>
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