Re: [syzbot] [gfs2?] UBSAN: shift-out-of-bounds in gfs2_dir_read (2)

[Andrew Price <anprice@redhat.com>]

On 14/07/2025 19:31, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    347e9f5043c8 Linux 6.16-rc6
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11afb18c580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f62a2ef17395702a
> dashboard link: https://syzkaller.appspot.com/bug?extid=4708579bb230a0582a57
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=172470f0580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16d0fd82580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-347e9f50.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/49ae91eb36e0/vmlinux-347e9f50.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/78497f74bd6b/bzImage-347e9f50.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/2445b7dba270/mount_0.gz
>   fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=15d7918c580000)
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+4708579bb230a0582a57@syzkaller.appspotmail.com
> 
> gfs2: fsid=syz:syz: Now mounting FS (format 1801)...
> gfs2: fsid=syz:syz.s: journal 0 mapped with 5 extents in 0ms
> gfs2: fsid=syz:syz.s: first mount done, others may mount
> ------------[ cut here ]------------
> UBSAN: shift-out-of-bounds in fs/gfs2/dir.c:1544:15
> shift exponent 32 is too large for 32-bit type 'u32' (aka 'unsigned int')
> CPU: 0 UID: 0 PID: 5508 Comm: syz.0.16 Not tainted 6.16.0-rc6-syzkaller #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> 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
>  dir_e_read fs/gfs2/dir.c:1544 [inline]
>  gfs2_dir_read+0x1730/0x1780 fs/gfs2/dir.c:1585
>  gfs2_readdir+0x14c/0x1b0 fs/gfs2/file.c:116
>  iterate_dir+0x5ac/0x770 fs/readdir.c:108
>  __do_sys_getdents64 fs/readdir.c:410 [inline]
>  __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
>  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: 0033:0x7f9672d8e929
> 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:00007ffd2be2c848 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
> RAX: ffffffffffffffda RBX: 00007f9672fb5fa0 RCX: 00007f9672d8e929
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
> RBP: 00007f9672e10b39 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f9672fb5fa0 R14: 00007f9672fb5fa0 R15: 0000000000000003
>  </TASK>
> ---[ end trace ]---
> 
> 
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
> 

#syz test

--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -450,6 +450,10 @@ static int gfs2_dinode_in(struct gfs2_inode *ip, const void *buf)
                gfs2_consist_inode(ip);
                return -EIO;
        }
+       if ((ip->i_diskflags & GFS2_DIF_EXHASH) && depth < ilog2(sdp->sd_hash_ptrs)) {
+               gfs2_consist_inode(ip);
+               return -EIO;
+       }
        ip->i_depth = (u8)depth;
        ip->i_entries = be32_to_cpu(str->di_entries);