linux-ext4 - Re: [PATCH] ext4: fix possible overflow in ext4_trim

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Date:	Tue, 06 Sep 2011 12:15:45 +0800
From:	Tao Ma <tm@....ma>
To:	Lukas Czerner <lczerner@...hat.com>
CC:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH] ext4: fix possible overflow in ext4_trim_fs()

Hi Lucas,
On 09/05/2011 10:34 PM, Lukas Czerner wrote:
> In ext4_trim_fs it is possible that start+len might overflow. Fix it by
> decrementing the len so that start+len equals to the file system size in
> the worst case.
Actually start + len can never overflow since they are changed by
start = range->start >> sb->s_blocksize_bits;
len = range->len >> sb->s_blocksize_bits;

range->start and range->len are u64, and after they are shifted with
blocksize_bits, start+len(ext4_fsblk_t is also 64bit) can't overflow.

Thanks
Tao
> 
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> ---
>  fs/ext4/mballoc.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 17a5a57..d86dc14 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4952,14 +4952,18 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
>  	uint64_t start, len, 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;
>  	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 (unlikely(len > max_blks))
> +		len = max_blks - start;
>  	if (start + len <= first_data_blk)
>  		goto out;
>  	if (start < first_data_blk) {

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