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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Mon, 24 Apr 2023 10:27:46 +0200
Message-ID: <CACT4Y+arm0wqa=GbrTpH4UJrc-OCq3dwvTKa9k-yxoPLtwnbHQ@mail.gmail.com>
Subject: Re: [syzbot] [fs?] KCSAN: data-race in inotify_handle_inode_event / inotify_remove_from_idr
To:     syzbot <syzbot+4a06d4373fd52f0b2f9c@syzkaller.appspotmail.com>
Cc:     amir73il@gmail.com, jack@suse.cz, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
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On Mon, 24 Apr 2023 at 10:09, syzbot
<syzbot+4a06d4373fd52f0b2f9c@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    622322f53c6d Merge tag 'mips-fixes_6.3_2' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1482ffafc80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fa4baf7c6b35b5d5
> dashboard link: https://syzkaller.appspot.com/bug?extid=4a06d4373fd52f0b2f9c
> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/8b5f31d96315/disk-622322f5.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/adca7dc8daae/vmlinux-622322f5.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/ed78ddc31ccb/bzImage-622322f5.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+4a06d4373fd52f0b2f9c@syzkaller.appspotmail.com

If I am reading this correctly, userspace can get wd=-1 as the result
of this race. Docs say wd must refer to a previously allocated
descriptor, which is positive. I don't see any mentions of semantics
of wd=-1.

> ==================================================================
> BUG: KCSAN: data-race in inotify_handle_inode_event / inotify_remove_from_idr
>
> write to 0xffff888104e31368 of 4 bytes by task 3229 on cpu 1:
>  inotify_remove_from_idr+0x106/0x310 fs/notify/inotify/inotify_user.c:511
>  inotify_ignored_and_remove_idr+0x34/0x60 fs/notify/inotify/inotify_user.c:532
>  inotify_freeing_mark+0x1d/0x30 fs/notify/inotify/inotify_fsnotify.c:133
>  fsnotify_free_mark fs/notify/mark.c:490 [inline]
>  fsnotify_destroy_mark+0x17a/0x190 fs/notify/mark.c:499
>  __do_sys_inotify_rm_watch fs/notify/inotify/inotify_user.c:817 [inline]
>  __se_sys_inotify_rm_watch+0xf7/0x170 fs/notify/inotify/inotify_user.c:794
>  __x64_sys_inotify_rm_watch+0x31/0x40 fs/notify/inotify/inotify_user.c:794
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> read to 0xffff888104e31368 of 4 bytes by task 3638 on cpu 0:
>  inotify_handle_inode_event+0x17e/0x2c0 fs/notify/inotify/inotify_fsnotify.c:113
>  fsnotify_handle_inode_event+0x19b/0x1f0 fs/notify/fsnotify.c:264
>  fsnotify_handle_event fs/notify/fsnotify.c:316 [inline]
>  send_to_group fs/notify/fsnotify.c:364 [inline]
>  fsnotify+0x101c/0x1150 fs/notify/fsnotify.c:570
>  __fsnotify_parent+0x307/0x480 fs/notify/fsnotify.c:230
>  fsnotify_parent include/linux/fsnotify.h:77 [inline]
>  fsnotify_file include/linux/fsnotify.h:99 [inline]
>  fsnotify_close include/linux/fsnotify.h:341 [inline]
>  __fput+0x4b0/0x570 fs/file_table.c:307
>  ____fput+0x15/0x20 fs/file_table.c:349
>  task_work_run+0x123/0x160 kernel/task_work.c:179
>  resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
>  exit_to_user_mode_loop+0xd1/0xe0 kernel/entry/common.c:171
>  exit_to_user_mode_prepare+0x6c/0xb0 kernel/entry/common.c:204
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:286 [inline]
>  syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:297
>  do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> value changed: 0x00000060 -> 0xffffffff
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 PID: 3638 Comm: syz-executor.0 Not tainted 6.3.0-rc7-syzkaller-00191-g622322f53c6d #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
> ==================================================================
>
>
> ---
> 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@googlegroups.com.
>
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