linux-kernel - Re: Slab out of bounds in setxattr

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Message-ID: <CAB+yDaZFZhku34wp-t_i32Vy6cYB9fnS0iboPnQZ26sQeAZ+Uw@mail.gmail.com>
Date:   Fri, 1 Jun 2018 21:06:49 -0700
From:   shankarapailoor <shankarapailoor@...il.com>
To:     shaggy@...nel.org
Cc:     jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: Slab out of bounds in setxattr

Hi,

Looking at the crash some more, it seems that if value_len > PAGE_SIZE
then e_buf->max_size is rounded up nearest page size [1]. If a new
attribute is added with value_len < e_buf->max_size - EA_SIZE(ea) then
no new space is allocated for the attiribute list [2] and this
triggers the KASAN slab out of bounds error. This is the case in the C
repro I provided.


1. https://elixir.bootlin.com/linux/v4.17-rc7/source/fs/jfs/xattr.c#L501
2. https://elixir.bootlin.com/linux/v4.17-rc7/source/fs/jfs/xattr.c#L723

On Fri, Jun 1, 2018 at 1:52 PM, shankarapailoor
<shankarapailoor@...il.com> wrote:
> Hi Dave et al,
>
> I have been fuzzing linux 4.17-rc4 with JFS using Syzkaller  KASAN:
> slab-out-of-bounds in jfs_xattr.
>
> Attached are my kernel configs and a C reproducer. In the first
> setxattr call it appears that length is much larger than the name. In
> __jfs_setxattr, I don't see where the length is checked against the
> actual value length.
>
> Regards,
> Shankara Pailoor



-- 
Regards,
Shankara Pailoor