Message-ID: <20241112115059.ecvomkalee5m4i4i@quack3>
Date: Tue, 12 Nov 2024 12:50:59 +0100
From: Jan Kara <jack@...e.cz>
To: syzbot <syzbot+318aab2cf26bb7d40228@...kaller.appspotmail.com>
Cc: amir73il@...il.com, jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, repnop@...gle.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fs?] WARNING in fanotify_handle_event (2)

On Mon 11-11-24 20:21:27, syzbot wrote:
> HEAD commit:    906bd684e4b1 Merge tag 'spi-fix-v6.12-rc6' of git://git.ke..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=177d4ea7980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=64aa0d9945bd5c1
> dashboard link: https://syzkaller.appspot.com/bug?extid=318aab2cf26bb7d40228
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1168dd87980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10fd4ea7980000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-906bd684.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/88c5c4ba7e33/vmlinux-906bd684.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/07094e69f47b/bzImage-906bd684.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/643aa6b4830a/mount_0.gz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+318aab2cf26bb7d40228@...kaller.appspotmail.com
> 
> loop0: detected capacity change from 0 to 128
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5308 at fs/notify/fanotify/fanotify.h:216 fanotify_info_copy_name fs/notify/fanotify/fanotify.h:216 [inline]
> WARNING: CPU: 0 PID: 5308 at fs/notify/fanotify/fanotify.h:216 fanotify_alloc_name_event fs/notify/fanotify/fanotify.c:646 [inline]
> WARNING: CPU: 0 PID: 5308 at fs/notify/fanotify/fanotify.h:216 fanotify_alloc_event fs/notify/fanotify/fanotify.c:810 [inline]
> WARNING: CPU: 0 PID: 5308 at fs/notify/fanotify/fanotify.h:216 fanotify_handle_event+0x2eba/0x3c50 fs/notify/fanotify/fanotify.c:936

Interesting. So this is complaining that the dentry name is longer than
NAME_MAX and checking the code, indeed VFS supports names upto PATH_MAX,
only individual filesystems limit them further to something smaller. So I
think we need to go though fanotify and make sure we are able to
accommodate names up to PATH_MAX (which is going to be somewhat non-trivial
because the resulting name event can be longer than PAGE_SIZE but I'd just
use kvmalloc() to make things simpler - in practice such events do not
really exist because so far nobody reported the WARNING would trigger).

								Honza

> Modules linked in:
> CPU: 0 UID: 0 PID: 5308 Comm: syz-executor207 Not tainted 6.12.0-rc6-syzkaller-00169-g906bd684e4b1 #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:fanotify_info_copy_name fs/notify/fanotify/fanotify.h:216 [inline]
> RIP: 0010:fanotify_alloc_name_event fs/notify/fanotify/fanotify.c:646 [inline]
> RIP: 0010:fanotify_alloc_event fs/notify/fanotify/fanotify.c:810 [inline]
> RIP: 0010:fanotify_handle_event+0x2eba/0x3c50 fs/notify/fanotify/fanotify.c:936
> Code: f6 ff ff e8 58 a4 6e ff 90 0f 0b 90 e9 c0 f7 ff ff e8 4a a4 6e ff 90 0f 0b 90 4c 8b 6c 24 10 e9 e7 f8 ff ff e8 37 a4 6e ff 90 <0f> 0b 90 4c 8b 6c 24 10 e9 04 fb ff ff e8 24 a4 6e ff 90 0f 0b 90
> RSP: 0018:ffffc9000d0473e0 EFLAGS: 00010293
> RAX: ffffffff82263629 RBX: ffffc9000d047844 RCX: ffff888000848000
> RDX: 0000000000000000 RSI: 0000000000000ffd RDI: 00000000000000ff
> RBP: ffffc9000d0475e0 R08: ffffffff82262f60 R09: 0000000000000000
> R10: ffff888043bd8038 R11: ffffffff821d7890 R12: ffff888043bd8000
> R13: 0000000000000ffd R14: ffff888043bd8000 R15: dffffc0000000000
> FS:  0000555581eb6380(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020004000 CR3: 000000003600e000 CR4: 0000000000352ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  send_to_group fs/notify/fsnotify.c:394 [inline]
>  fsnotify+0x1657/0x1f60 fs/notify/fsnotify.c:607
>  __fsnotify_parent+0x4f5/0x5e0 fs/notify/fsnotify.c:264
>  fsnotify_parent include/linux/fsnotify.h:96 [inline]
>  fsnotify_file include/linux/fsnotify.h:131 [inline]
>  fsnotify_open include/linux/fsnotify.h:401 [inline]
>  vfs_open+0x28d/0x330 fs/open.c:1095
>  do_open fs/namei.c:3774 [inline]
>  path_openat+0x2c84/0x3590 fs/namei.c:3933
>  do_filp_open+0x235/0x490 fs/namei.c:3960
>  do_sys_openat2+0x13e/0x1d0 fs/open.c:1415
>  do_sys_open fs/open.c:1430 [inline]
>  __do_sys_creat fs/open.c:1508 [inline]
>  __se_sys_creat fs/open.c:1502 [inline]
>  __x64_sys_creat+0x123/0x170 fs/open.c:1502
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fde2034f6b9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 17 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fff3d0c3658 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
> RAX: ffffffffffffffda RBX: 00007fff3d0c3828 RCX: 00007fde2034f6b9
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020003500
> RBP: 00007fde203c3610 R08: 00007fff3d0c3828 R09: 00007fff3d0c3828
> R10: 00007fff3d0c3828 R11: 0000000000000246 R12: 0000000000000001
> R13: 00007fff3d0c3818 R14: 0000000000000001 R15: 0000000000000001
>  </TASK>
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> 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.
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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