Re: [PATCH V2] squashfs: Add length check in squashfs_symlink_read_folio

[Lizhi Xu]

On Thu, 1 Aug 2024 17:30:42 +0200, Jan Kara wrote:
> > syzbot report KMSAN: uninit-value in pick_link, the root cause is that
> > squashfs_symlink_read_folio did not check the length, resulting in folio
> > not being initialized and did not return the corresponding error code.
> > 
> > The incorrect value of length is due to the incorrect value of inode->i_size.
> > 
> > Reported-and-tested-by: syzbot+24ac24ff58dc5b0d26b9@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Closes: https://syzkaller.appspot.com/bug?extid=24ac24ff58dc5b0d26b9
> > Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
> > ---
> >  fs/squashfs/symlink.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/fs/squashfs/symlink.c b/fs/squashfs/symlink.c
> > index 6ef735bd841a..d5fa5165ddd6 100644
> > --- a/fs/squashfs/symlink.c
> > +++ b/fs/squashfs/symlink.c
> > @@ -61,6 +61,12 @@ static int squashfs_symlink_read_folio(struct file *file, struct folio *folio)
> >  		}
> >  	}
> >  
> > +	if (length < 0) {
> 
> OK, so this would mean that (int)inode->i_size is a negative number.
> Possible. Perhaps we should rather better validate i_size of symlinks in
> squashfs_read_inode()? Otherwise it would be a whack-a-mole game of
> catching places that get confused by bogus i_size...
This move is tough enough, start from where i_size is initialized.
I will send a v3 patch for it.

--
Lizhi