linux-kernel - Re: [syzbot] [ext4?] kernel panic: EXT4-fs (device loop0): panic forced after error (2)

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Date:   Wed, 28 Dec 2022 18:15:09 -0500
From:   "Theodore Ts'o" <tytso@....edu>
To:     syzbot <syzbot+3c45794f522ad93b0eb6@...kaller.appspotmail.com>
Cc:     adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        nathan@...nel.org, ndesaulniers@...gle.com,
        syzkaller-bugs@...glegroups.com, trix@...hat.com
Subject: Re: [syzbot] [ext4?] kernel panic: EXT4-fs (device loop0): panic
 forced after error (2)

On Wed, Dec 28, 2022 at 12:16:41PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    72a85e2b0a1e Merge tag 'spi-fix-v6.2-rc1' of git://git.ker..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=13527f8c480000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4e2d7bfa2d6d5a76
> dashboard link: https://syzkaller.appspot.com/bug?extid=3c45794f522ad93b0eb6
> compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12d7f2e4480000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10c8d2ac480000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/510d16df06c8/disk-72a85e2b.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/50ef5477a1d4/vmlinux-72a85e2b.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/f2acd6f1189a/bzImage-72a85e2b.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/6f0bbc430a64/mount_0.gz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3c45794f522ad93b0eb6@...kaller.appspotmail.com
> 
> loop0: detected capacity change from 0 to 512
> EXT4-fs error (device loop0): ext4_map_blocks:607: inode #2: block 2: comm syz-executor170: lblock 0 mapped to illegal pblock 2 (length 1)
> Kernel panic - not syncing: EXT4-fs (device loop0): panic forced after error

So this is a totally bogus Syzbot report.  If you use the mount option
"errors=panic", and you feed ext4 a corrupted file system, then it
*will* issue an "Ext4-fs error" message, and if you tell it to panic,
it will panic.

So *please* let's not have some crazy Red Hat principal engineer try
to file this as a high severity CVE....

This is Working As Intended.  And it is Not A Bug.

     		   	      	     	- Ted