linux-ext4 - Re: [RFC 1/1] ext4: Fix overflow case for map.m_len in ext4_iomap_begin

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Date:   Tue, 14 Apr 2020 17:50:13 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     jack@...e.cz, tytso@....edu, linux-ext4@...r.kernel.org,
        adilger@...ger.ca, darrick.wong@...cle.com, hch@...radead.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, willy@...radead.org,
        linux-unionfs@...r.kernel.org,
        syzbot+77fa5bdb65cc39711820@...kaller.appspotmail.com
Subject: Re: [RFC 1/1] ext4: Fix overflow case for map.m_len in
 ext4_iomap_begin_*

On Sun 12-04-20 14:54:35, Ritesh Harjani wrote:
> EXT4_MAX_LOGICAL_BLOCK - map.m_lblk + 1 in case when
> map.m_lblk (offset) is 0 could overflow an unsigned int
> and become 0.
> 
> Fix this.
> 
> Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> Reported-by: syzbot+77fa5bdb65cc39711820@...kaller.appspotmail.com
> Fixes: d3b6f23f7167 ("ext4: move ext4_fiemap to use iomap framework")

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/inode.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index e416096fc081..d630ec7a9c8e 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3424,6 +3424,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  	int ret;
>  	struct ext4_map_blocks map;
>  	u8 blkbits = inode->i_blkbits;
> +	loff_t len;
>  
>  	if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
>  		return -EINVAL;
> @@ -3435,8 +3436,11 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  	 * Calculate the first and last logical blocks respectively.
>  	 */
>  	map.m_lblk = offset >> blkbits;
> -	map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
> +	len = min_t(loff_t, (offset + length - 1) >> blkbits,
>  			  EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
> +	if (len > EXT4_MAX_LOGICAL_BLOCK)
> +		len = EXT4_MAX_LOGICAL_BLOCK;
> +	map.m_len = len;
>  
>  	if (flags & IOMAP_WRITE)
>  		ret = ext4_iomap_alloc(inode, &map, flags);
> @@ -3524,6 +3528,7 @@ static int ext4_iomap_begin_report(struct inode *inode, loff_t offset,
>  	bool delalloc = false;
>  	struct ext4_map_blocks map;
>  	u8 blkbits = inode->i_blkbits;
> +	loff_t len
>  
>  	if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
>  		return -EINVAL;
> @@ -3541,8 +3546,11 @@ static int ext4_iomap_begin_report(struct inode *inode, loff_t offset,
>  	 * Calculate the first and last logical block respectively.
>  	 */
>  	map.m_lblk = offset >> blkbits;
> -	map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
> +	len = min_t(loff_t, (offset + length - 1) >> blkbits,
>  			  EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
> +	if (len > EXT4_MAX_LOGICAL_BLOCK)
> +		len = EXT4_MAX_LOGICAL_BLOCK;
> +	map.m_len = len;
>  
>  	/*
>  	 * Fiemap callers may call for offset beyond s_bitmap_maxbytes.
> -- 
> 2.21.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR