linux-kernel - Re: [PATCH] filemap: Init the newly allocated folio memory to 0 for the filemap

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Message-ID: <20240801025842.GM5334@ZenIV>
Date: Thu, 1 Aug 2024 03:58:42 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Lizhi Xu <lizhi.xu@...driver.com>
Cc: syzbot+24ac24ff58dc5b0d26b9@...kaller.appspotmail.com,
	brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, phillip@...ashfs.org.uk,
	squashfs-devel@...ts.sourceforge.net,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] filemap: Init the newly allocated folio memory to 0 for
 the filemap

On Thu, Aug 01, 2024 at 10:27:39AM +0800, Lizhi Xu wrote:
> syzbot report KMSAN: uninit-value in pick_link, this is because the
> corresponding folio was not found from the mapping, and the memory was
> not initialized when allocating a new folio for the filemap.
> 
> To avoid the occurrence of kmsan report uninit-value, initialize the
> newly allocated folio memory to 0.

NAK.

You are papering over the real bug here.

That page either
	* has been returned by find_get_page(), cached, uptodate and
with uninitialized contents or
	* has been returned by successful read_mapping_page() - and
left with uninitialized contents or
	* had inode->i_size in excess of initialized contents.

I'd suggest bisecting that.