From: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Subject: Re: [PATCH] ext4: ext4_mb_seq_groups_show: Fix stack memory corruption
Date: Thu, 10 Nov 2016 11:14:17 +0530
Message-ID: <6088605.ZfrVhX6KQh@localhost.localdomain>
References: <1478501141-15651-1-git-send-email-chandan@linux.vnet.ibm.com> <20161108092115.GG32353@quack2.suse.cz>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7Bit
Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, adilger@dilger.ca
To: Jan Kara <jack@suse.cz>
In-Reply-To: <20161108092115.GG32353@quack2.suse.cz>
Sender: linux-ext4-owner@vger.kernel.org

On Tuesday, November 08, 2016 10:21:15 AM Jan Kara wrote:
> On Mon 07-11-16 12:15:41, Chandan Rajendra wrote:
> > The number of 'counters' elements needed in 'struct sg' is
> > super_block->s_blocksize_bits + 2. Presently we have 16 'counters'
> > elements in the array. This is insufficient for block sizes >= 32k. In
> > such cases the memcpy operation performed in ext4_mb_seq_groups_show()
> > would cause stack memory corruption.
> > 
> > Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
> > ---
> >  fs/ext4/mballoc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index a937ac7..67e6fcb 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -2287,7 +2287,7 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
> >  	struct ext4_group_info *grinfo;
> >  	struct sg {
> >  		struct ext4_group_info info;
> > -		ext4_grpblk_t counters[16];
> > +		ext4_grpblk_t counters[16 + 2];
> 
> How about using EXT4_MAX_BLOCK_LOG_SIZE + 2? It would be somewhat clearer
> what that means...  Having a function returning number of buddy counters in
> a group info would be even better (and a constant for maximum number of
> counters) but that's an independent cleanup...

Sorry about the late reply. I will send out V2 with the fix. Also, I will work
on the cleanup patch and send it out soon.

-- 
chandan