[PATCH v3] ext4: fix possible overflow in ext4_trim_fs()

[PATCH v3] ext4: fix possible overflow in ext4_trim_fs()

[Lukas Czerner]

The overflow can happen when we are calling get_group_no_and_offset()
which stores the result of do_div() in 32 bit long type. However the
result might be bigger than that if big blocknr is passed in. This will
most likely happen when calling FITRIM with the default argument len =
ULLONG_MAX.

Fix this by using "end" variable instead of "start+len" as it is easier
to get right and specifically check that the end is not beyond the end
of the file system, so we are sure that the result of
get_group_no_and_offset() will not overflow. Otherwise truncate it to
the size of the file system.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
---
v2 - Change commit description to better describe the problem
v3 - Use end instead of start+len, rework the fix

 fs/ext4/mballoc.c |   43 +++++++++++++++++++++++--------------------
 1 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 17a5a57..fa8b14b 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4946,37 +4946,36 @@ out:
 int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
 {
 	struct ext4_group_info *grp;
-	ext4_group_t first_group, last_group;
-	ext4_group_t group, ngroups = ext4_get_groups_count(sb);
+	ext4_group_t group, first_group, last_group;
 	ext4_grpblk_t cnt = 0, first_block, last_block;
-	uint64_t start, len, minlen, trimmed = 0;
+	uint64_t start, end, minlen, trimmed = 0;
 	ext4_fsblk_t first_data_blk =
 			le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
+	ext4_fsblk_t max_blks = ext4_blocks_count(EXT4_SB(sb)->s_es);
 	int ret = 0;
 
 	start = range->start >> sb->s_blocksize_bits;
-	len = range->len >> sb->s_blocksize_bits;
+	end = start + (range->len >> sb->s_blocksize_bits) - 1;
 	minlen = range->minlen >> sb->s_blocksize_bits;
 
-	if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)))
+	if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)) ||
+	    unlikely(start > max_blks))
 		return -EINVAL;
-	if (start + len <= first_data_blk)
+	if (unlikely(end >= max_blks))
+		end = max_blks - 1;
+	if (end <= first_data_blk)
 		goto out;
-	if (start < first_data_blk) {
-		len -= first_data_blk - start;
+	if (start < first_data_blk)
 		start = first_data_blk;
-	}
 
 	/* Determine first and last group to examine based on start and len */
 	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) start,
 				     &first_group, &first_block);
-	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) (start + len),
+	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) end,
 				     &last_group, &last_block);
-	last_group = (last_group > ngroups - 1) ? ngroups - 1 : last_group;
-	last_block = EXT4_BLOCKS_PER_GROUP(sb);
 
-	if (first_group > last_group)
-		return -EINVAL;
+	/* The last block to discard in the group */
+	end = EXT4_BLOCKS_PER_GROUP(sb);
 
 	for (group = first_group; group <= last_group; group++) {
 		grp = ext4_get_group_info(sb, group);
@@ -4990,22 +4989,26 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
 		/*
 		 * For all the groups except the last one, last block will
 		 * always be EXT4_BLOCKS_PER_GROUP(sb), so we only need to
-		 * change it for the last group in which case start +
-		 * len < EXT4_BLOCKS_PER_GROUP(sb).
+		 * change it for the last group, note that last_block is
+		 * already computed earlier by ext4_get_group_no_and_offset()
 		 */
-		if (first_block + len < EXT4_BLOCKS_PER_GROUP(sb))
-			last_block = first_block + len;
-		len -= last_block - first_block;
+		if (group == last_group)
+			end = last_block;
 
 		if (grp->bb_free >= minlen) {
 			cnt = ext4_trim_all_free(sb, group, first_block,
-						last_block, minlen);
+						end, minlen);
 			if (cnt < 0) {
 				ret = cnt;
 				break;
 			}
 		}
 		trimmed += cnt;
+
+		/*
+		 * For every group except the first one, we are sure
+		 * that the first block to discard will be block #0.
+		 */
 		first_block = 0;
 	}
 	range->len = trimmed * sb->s_blocksize;
-- 
1.7.4.4

Re: [PATCH v3] ext4: fix possible overflow in ext4_trim_fs()

[Lukas Czerner]

On Wed, 7 Sep 2011, Lukas Czerner wrote:

> The overflow can happen when we are calling get_group_no_and_offset()
> which stores the result of do_div() in 32 bit long type. However the
> result might be bigger than that if big blocknr is passed in. This will
> most likely happen when calling FITRIM with the default argument len =
> ULLONG_MAX.
> 
> Fix this by using "end" variable instead of "start+len" as it is easier
> to get right and specifically check that the end is not beyond the end
> of the file system, so we are sure that the result of
> get_group_no_and_offset() will not overflow. Otherwise truncate it to
> the size of the file system.

Any comments on this ? Note that the test case will be in xfstests soon.

http://www.spinics.net/lists/xfs/msg07251.html

Thanks!
-Lukas


> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> ---
> v2 - Change commit description to better describe the problem
> v3 - Use end instead of start+len, rework the fix
> 
>  fs/ext4/mballoc.c |   43 +++++++++++++++++++++++--------------------
>  1 files changed, 23 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 17a5a57..fa8b14b 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4946,37 +4946,36 @@ out:
>  int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
>  {
>  	struct ext4_group_info *grp;
> -	ext4_group_t first_group, last_group;
> -	ext4_group_t group, ngroups = ext4_get_groups_count(sb);
> +	ext4_group_t group, first_group, last_group;
>  	ext4_grpblk_t cnt = 0, first_block, last_block;
> -	uint64_t start, len, minlen, trimmed = 0;
> +	uint64_t start, end, minlen, trimmed = 0;
>  	ext4_fsblk_t first_data_blk =
>  			le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
> +	ext4_fsblk_t max_blks = ext4_blocks_count(EXT4_SB(sb)->s_es);
>  	int ret = 0;
>  
>  	start = range->start >> sb->s_blocksize_bits;
> -	len = range->len >> sb->s_blocksize_bits;
> +	end = start + (range->len >> sb->s_blocksize_bits) - 1;
>  	minlen = range->minlen >> sb->s_blocksize_bits;
>  
> -	if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)))
> +	if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)) ||
> +	    unlikely(start > max_blks))
>  		return -EINVAL;
> -	if (start + len <= first_data_blk)
> +	if (unlikely(end >= max_blks))
> +		end = max_blks - 1;
> +	if (end <= first_data_blk)
>  		goto out;
> -	if (start < first_data_blk) {
> -		len -= first_data_blk - start;
> +	if (start < first_data_blk)
>  		start = first_data_blk;
> -	}
>  
>  	/* Determine first and last group to examine based on start and len */
>  	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) start,
>  				     &first_group, &first_block);
> -	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) (start + len),
> +	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) end,
>  				     &last_group, &last_block);
> -	last_group = (last_group > ngroups - 1) ? ngroups - 1 : last_group;
> -	last_block = EXT4_BLOCKS_PER_GROUP(sb);
>  
> -	if (first_group > last_group)
> -		return -EINVAL;
> +	/* The last block to discard in the group */
> +	end = EXT4_BLOCKS_PER_GROUP(sb);
>  
>  	for (group = first_group; group <= last_group; group++) {
>  		grp = ext4_get_group_info(sb, group);
> @@ -4990,22 +4989,26 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
>  		/*
>  		 * For all the groups except the last one, last block will
>  		 * always be EXT4_BLOCKS_PER_GROUP(sb), so we only need to
> -		 * change it for the last group in which case start +
> -		 * len < EXT4_BLOCKS_PER_GROUP(sb).
> +		 * change it for the last group, note that last_block is
> +		 * already computed earlier by ext4_get_group_no_and_offset()
>  		 */
> -		if (first_block + len < EXT4_BLOCKS_PER_GROUP(sb))
> -			last_block = first_block + len;
> -		len -= last_block - first_block;
> +		if (group == last_group)
> +			end = last_block;
>  
>  		if (grp->bb_free >= minlen) {
>  			cnt = ext4_trim_all_free(sb, group, first_block,
> -						last_block, minlen);
> +						end, minlen);
>  			if (cnt < 0) {
>  				ret = cnt;
>  				break;
>  			}
>  		}
>  		trimmed += cnt;
> +
> +		/*
> +		 * For every group except the first one, we are sure
> +		 * that the first block to discard will be block #0.
> +		 */
>  		first_block = 0;
>  	}
>  	range->len = trimmed * sb->s_blocksize;
> 

-- 

Re: [PATCH v3] ext4: fix possible overflow in ext4_trim_fs()

[Ted Ts'o]

On Wed, Sep 07, 2011 at 05:52:57PM +0200, Lukas Czerner wrote:
> The overflow can happen when we are calling get_group_no_and_offset()
> which stores the result of do_div() in 32 bit long type. However the
> result might be bigger than that if big blocknr is passed in. This will
> most likely happen when calling FITRIM with the default argument len =
> ULLONG_MAX.
> 
> Fix this by using "end" variable instead of "start+len" as it is easier
> to get right and specifically check that the end is not beyond the end
> of the file system, so we are sure that the result of
> get_group_no_and_offset() will not overflow. Otherwise truncate it to
> the size of the file system.
> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>

Hi Lukas,

Since I've merged the bigalloc patches that uses clusters instead of
blocks for various file system parameters.  I made a quick attempt to
port your patch, and it wasn't obvious (and I don't have your testing
framework).  Could you do me a favor and forward port your patch to
either the dev or master branch on the ext4 github repository?

Thanks!!

					- Ted

Re: [PATCH v3] ext4: fix possible overflow in ext4_trim_fs()

[Lukas Czerner]

On Mon, 10 Oct 2011, Ted Ts'o wrote:

> On Wed, Sep 07, 2011 at 05:52:57PM +0200, Lukas Czerner wrote:
> > The overflow can happen when we are calling get_group_no_and_offset()
> > which stores the result of do_div() in 32 bit long type. However the
> > result might be bigger than that if big blocknr is passed in. This will
> > most likely happen when calling FITRIM with the default argument len =
> > ULLONG_MAX.
> > 
> > Fix this by using "end" variable instead of "start+len" as it is easier
> > to get right and specifically check that the end is not beyond the end
> > of the file system, so we are sure that the result of
> > get_group_no_and_offset() will not overflow. Otherwise truncate it to
> > the size of the file system.
> > 
> > Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> 
> Hi Lukas,
> 
> Since I've merged the bigalloc patches that uses clusters instead of
> blocks for various file system parameters.  I made a quick attempt to
> port your patch, and it wasn't obvious (and I don't have your testing
> framework).  Could you do me a favor and forward port your patch to
> either the dev or master branch on the ext4 github repository?
> 
> Thanks!!
> 
> 					- Ted

Hi Ted,

no problem, I'll do that. Btw, the test case for it is already in
xfstests (260) so I'll mention that in the commit description as well.

Thanks!
-Lukas