linux-ext4 - Re: [PATCH 1/4] ext4: fix trim length underflow with small trim length.

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Message-ID: <alpine.LFD.2.00.1107011218290.4168@dhcp-27-109.brq.redhat.com>
Date:	Fri, 1 Jul 2011 12:20:06 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Tao Ma <tm@....ma>
cc:	Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/4] ext4: fix trim length underflow with small trim
 length.

On Fri, 1 Jul 2011, Tao Ma wrote:

> Hi Lukas,
> On 07/01/2011 05:45 PM, Lukas Czerner wrote:
> > On Thu, 30 Jun 2011, Tao Ma wrote:
> > 
> >> From: Tao Ma <boyu.mt@...bao.com>
> >>
> >> In 0f0a25b, we adjust 'len' with s_first_data_block - start, but
> >> it could underflow in case blocksize=1K, fstrim_range.len=512 and
> >> fstrim_range.start = 0. In this case, when we run the code:
> >> len -= first_data_blk - start; len will be underflow to -1ULL.
> >> In the end, although we are safe that last_group check later will limit
> >> the trim to the whole volume, but that isn't what the user really want.
> >>
> >> So this patch fix it. It also adds the check for 'start' like ext3 so that
> >> we can break immediately if the start is invalid.
> > 
> > Hi Tao,
> > 
> > thanks for the resend!
> > 
> >>
> >> Signed-off-by: Tao Ma <boyu.mt@...bao.com>
> >> ---
> >>  fs/ext4/mballoc.c |    4 ++++
> >>  1 files changed, 4 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> >> index 6ed859d..2336424 100644
> >> --- a/fs/ext4/mballoc.c
> >> +++ b/fs/ext4/mballoc.c
> >> @@ -4904,6 +4904,9 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
> >>  
> >>  	if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)))
> >>  		return -EINVAL;
> >> +	if (start >= ext4_blocks_count(EXT4_SB(sb)->s_es) ||
> >> +	    start + len <= first_data_blk)
> >> +		goto out;
> > 
> > We should really return -EINVAL in case that start is beyond the
> > filesystem. However we can not return -EINVAL in case that start+len is
> > before the first data block, because it would require user to know fs
> > internals.
> uh, actually I have checked what ext3 does and in case of start >
> block_count, ext3 returns 0, not EINVAL and I made it to work like ext3.
> So we should change it also?

I have already sent a patch a while ago. It should be in Jan's queue.

-Lukas

> 
> Thanks
> Tao
> > 
> > So simply doing this, should be enough:
> > 
> > 	if (start + len <= first_data_blk)
> > 		goto out;
> > 
> > and the code later
> > 
> > 	if (first_group > last_group)
> > 		return -EINVAL;
> > 
> > will handle the rest.
> > 
> > Thanks!
> > -Lukas
> > 
> > 
> >>  	if (start < first_data_blk) {
> >>  		len -= first_data_blk - start;
> >>  		start = first_data_blk;
> >> @@ -4952,5 +4955,6 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
> >>  	}
> >>  	range->len = trimmed * sb->s_blocksize;
> >>  
> >> +out:
> >>  	return ret;
> >>  }
> >>
> > 
> 
> 
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