linux-kernel - Re: [PATCH] Fix: ext4: add sanity check for inode inline write range

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Message-ID: <CAHxJ8O_HF9cy5mg-W77M02E=WHrMsSOTmyxZYogUut3jJgEyFQ@mail.gmail.com>
Date: Wed, 8 Oct 2025 16:40:09 +0300
From: Ahmet Eray Karadag <eraykrdg1@...il.com>
To: "Theodore Ts'o" <tytso@....edu>
Cc: adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, 
	linux-kernel@...r.kernel.org, david.hunter.linux@...il.com, 
	skhan@...uxfoundation.org, 
	syzbot+f3185be57d7e8dda32b8@...kaller.appspotmail.com, 
	Albin Babu Varghese <albinbabuvarghese20@...il.com>
Subject: Re: [PATCH] Fix: ext4: add sanity check for inode inline write range

Hi Ted,

Thanks for the feedback.

You’re right — the commit description didn’t match the actual change,
and I appreciate you pointing that out.
After reading Darrick’s reply, I realized our patch was only
preventing the final crash rather than fixing the underlying issue.
Sorry for the confusion — I noticed that a bit too late after sending it out.

I’ll review things more carefully before sending any follow-ups.

Thanks again for the guidance.

Best regards,
Eray

Theodore Ts'o <tytso@....edu>, 8 Eki 2025 Çar, 15:34 tarihinde şunu yazdı:
>
> On Wed, Oct 08, 2025 at 02:42:22AM +0300, Ahmet Eray Karadag wrote:
> > Add a simple check in ext4_try_to_write_inline_data() to prevent
> > writes that extend past the inode's inline data area. The function
> > now returns -EINVAL if pos + len exceeds i_inline_size.
>
> The commit description doesn't match with what the patch does.  The
> patch changes ext4_write_inline_data_end() and not
> ext4_try_to_write_inline().  Ext4_try_to_write_inline_data() called
> from ext4_write_begin(), and it does this:
>
>         if (pos + len > ext4_get_max_inline_size(inode))
>                 return ext4_convert_inline_data_to_extent(mapping, inode);
>
> So the write extends past the inline data area, in ext4_write_begin(),
> it will have already been converted to a non-inline function.
>
> The ext4_write_inline_data_end() function is called from
> ext4_write_end(), so you need to figure out why we hadn't configured
> the file away from inline data in ext4_write_begin().
>
> > Reported-by: syzbot+f3185be57d7e8dda32b8@...kaller.appspotmail.com
> > Link: https://syzkaller.appspot.com/bug?extid=f3185be57d7e8dda32b8
>
> Did you just randomly bash the code until the syzbot reproducer
> stopped failing?  Please try to understand the code and the failure
> much more deeply before attempting to change the code.
>
> Cheers,
>
>                                         - Ted