Re: [PATCH] ext4: Verify extent header in ext4_find_extent()

[Shigeru Yoshida]

On Mon, Jan 02, 2023 at 03:10:19PM -0800, Eric Biggers wrote:
> On Mon, Jan 02, 2023 at 02:58:33PM +0000, Shigeru Yoshida wrote:
> > syzbot reported use-after-free in ext4_find_extent() [1].  If there is
> > a corrupted file system, this can cause invalid memory access.
> > 
> > This patch fixes the issue by verifying extent header.
> > 
> > Reported-by: syzbot+bf4bb7731ef73b83a3b4@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Link: https://syzkaller.appspot.com/bug?id=cd95cb722bfa1234ac4c78345c8953ee2e7170d0 [1]
> > Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
> > ---
> >  fs/ext4/extents.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 9de1c9d1a13d..79bfa583ab1d 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -901,6 +901,9 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,
> >  		ret = -EFSCORRUPTED;
> >  		goto err;
> >  	}
> > +	ret = ext4_ext_check(inode, eh, depth, 0);
> > +	if (ret)
> > +		goto err;
> 
> This patch probably does not address the root cause of the problem.  Please see
> the discussion on the very similar patch
> https://lore.kernel.org/linux-ext4/20221230062931.2344157-1-tudor.ambarus@xxxxxxxxxx/T/#u

Thank you so much for your comment!!  I missed the discussion you
mentioned.  I'll check that.

Regards,
Shigeru

> 
> - Eric
>