linux-kernel - Re: [PATCH v2] ext4: mballoc: Fix spectre gadget in ext4_mb_regular

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Message-ID: <20180802040609.GD9187@thunk.org>
Date:   Thu, 2 Aug 2018 00:06:09 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jeremy Cline <jcline@...hat.com>
Cc:     Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] ext4: mballoc: Fix spectre gadget in
 ext4_mb_regular_allocator

On Mon, Jul 30, 2018 at 06:07:47PM +0000, Jeremy Cline wrote:
> 'ac->ac_g_ex.fe_len' is a user-controlled value which is used in the
> derivation of 'ac->ac_2order'. 'ac->ac_2order', in turn, is used to
> index arrays which makes it a potential spectre gadget. Fix this by
> sanitizing the value assigned to 'ac->ac2_order'.  This covers the
> following accesses found with the help of smatch:
> 
> * fs/ext4/mballoc.c:1896 ext4_mb_simple_scan_group() warn: potential
>   spectre issue 'grp->bb_counters' [w] (local cap)
> 
> * fs/ext4/mballoc.c:445 mb_find_buddy() warn: potential spectre issue
>   'EXT4_SB(e4b->bd_sb)->s_mb_offsets' [r] (local cap)
> 
> * fs/ext4/mballoc.c:446 mb_find_buddy() warn: potential spectre issue
>   'EXT4_SB(e4b->bd_sb)->s_mb_maxs' [r] (local cap)
> 
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: stable@...r.kernel.org
> Suggested-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Jeremy Cline <jcline@...hat.com>

Thanks, applied.

					- Ted