linux-kernel - Re: [PATCH] ext4: fix WARNING in lock_two

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Message-ID: <20231225021136.GC491196@mit.edu>
Date: Sun, 24 Dec 2023 21:11:36 -0500
From: "Theodore Ts'o" <tytso@....edu>
To: Baokun Li <libaokun1@...wei.com>
Cc: Edward Adam Davis <eadavis@...com>,
        syzbot+2c4a3b922a860084cc7f@...kaller.appspotmail.com,
        adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, yangerkun <yangerkun@...wei.com>
Subject: Re: [PATCH] ext4: fix WARNING in lock_two_nondirectories

On Mon, Dec 25, 2023 at 09:38:51AM +0800, Baokun Li wrote:
> Marking the boot loader inode as a bad inode here is useless,
> EXT4_IGET_BAD allows us to get a bad boot loader inode.
> In my opinion, it doesn't make sense to call lock_two_nondirectories()
> here to determine if the inode is a regular file or not, since the logic
> for dealing with non-regular files comes after the locking, so calling
> lock_two_inodes() directly here will suffice.

This is all very silly, and why I consider this sort of thing pure
syzkaller noise.  It really doesn't protect against any real threat,
and it encourages people to put all sorts of random crud in kernel
code, all in the name of trying to shut up syzbot.

If we *are* going to care about shutting up syzkaller, the right
approach is to simply add a check in swap_inode_boot_loader() which
causes it to call ext4_error() and declare the file system corrupted
if the bootloader inode is not a regular file, and then return
-EFSCORRUPTED.

We don't need to add random hacks to ext4_iget(), or in other places...

   	      	     	    	     - Ted