linux-kernel - Re: [PATCH] xfs: reject log records with v2 size but v1 header version to avoid OOB

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Message-ID: <aRWA7v5Yng5i4X1U@infradead.org>
Date: Wed, 12 Nov 2025 22:55:42 -0800
From: Christoph Hellwig <hch@...radead.org>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Raphael Pinsonneault-Thibeault <rpthibeault@...il.com>, cem@...nel.org,
	chandanbabu@...nel.org, bfoster@...hat.com,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev, skhan@...uxfoundation.org,
	syzbot+9f6d080dece587cfdd4c@...kaller.appspotmail.com
Subject: Re: [PATCH] xfs: reject log records with v2 size but v1 header
 version to avoid OOB

On Wed, Nov 12, 2025 at 10:45:04AM -0800, Darrick J. Wong wrote:
> > @@ -3064,8 +3064,12 @@ xlog_do_recovery_pass(
> >  		 * still allocate the buffer based on the incorrect on-disk
> >  		 * size.
> >  		 */
> > -		if (h_size > XLOG_HEADER_CYCLE_SIZE &&
> > -		    (rhead->h_version & cpu_to_be32(XLOG_VERSION_2))) {
> 
> Just out of curiosity, why is this a bit flag test?  Did XFS ever emit a
> log record with both XLOG_VERSION_2 *and* XLOG_VERSION_1 set?  The code
> that writes new log records only sets h_version to 1 or 2, not 3.

Yeah.  This particular instance got added by me, but it is a copy and
paste from xlog_logrec_hblks, which again consolidate multiple chunks
of this style of code, which were moved around a few times.

I think originally this came from Nathan fixing this:

-               if ((h_version && XLOG_VERSION_2) &&
+
+               if ((h_version & XLOG_VERSION_2) &&

or in other words, this was a mess all the way back.