linux-kernel - Re: Bug report - slab-out-of-bounds in vcs_scr

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Message-ID: <a0550a96-a7db-60d7-c4ac-86be8c8dd275@suse.com>
Date:   Tue, 5 Nov 2019 10:14:01 +0100
From:   Jiri Slaby <jslaby@...e.com>
To:     Or Cohen <orcohen@...oaltonetworks.com>
Cc:     Nicolas Pitre <nico@...xnic.net>,
        Greg KH <gregkh@...uxfoundation.org>, textshell@...uujin.de,
        Daniel Vetter <daniel.vetter@...ll.ch>, sam@...nborg.org,
        mpatocka@...hat.com, ghalat@...hat.com,
        linux-kernel@...r.kernel.org, jwilk@...lk.net,
        Nadav Markus <nmarkus@...oaltonetworks.com>,
        syzkaller@...glegroups.com
Subject: Re: Bug report - slab-out-of-bounds in vcs_scr_readw

On 05. 11. 19, 10:03, Or Cohen wrote:
> @Nicolas Pitre  - I agree with you, "vcs_size" may return a negative
> error code, so the patch is correct but as @jslaby@...e.com  said it
> won't fix the issue.
> In my debugging session, "vcs_size" returns a positive integer ( 8000
> decimal ) and the bug still triggers.
> 
> Maybe it's related to the following logic in "vcs_size"? ( not sure
> about that.. )
> 
> 221        if (use_attributes(inode)) {
> 222                if (use_unicode(inode))
> 223                        return -EOPNOTSUPP;
> 224                size = 2*size + HEADER_SIZE;
> 225       } else if (use_unicode(inode))
> 226               size *= 4;
> 227        return size;
> 
> Why in the case of "use_unicode(inode)" size is multiplied by 4 and
> not 2?  ( as we can see in line 224 )

Because unicode uses 4 bytes. The issue is that there is no handling for
unicode in vcs_write at all. (Compare with vcs_read.)

thanks,
-- 
js
suse labs