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Subject: Re: [RFC 1/1] ext4: Fix overflow case for map.m_len in
 ext4_iomap_begin_*
To:     Jan Kara <jack@suse.cz>
Cc:     tytso@mit.edu, linux-ext4@vger.kernel.org, adilger@dilger.ca,
        darrick.wong@oracle.com, hch@infradead.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-xfs@vger.kernel.org, willy@infradead.org,
        linux-unionfs@vger.kernel.org,
        syzbot+77fa5bdb65cc39711820@syzkaller.appspotmail.com
References: <00000000000048518b05a2fef23a@google.com>
 <dea98f0b07e16de219d8741c1fefc7cb476cb482.1586681010.git.riteshh@linux.ibm.com>
 <20200414155013.GF28226@quack2.suse.cz>
From:   Ritesh Harjani <riteshh@linux.ibm.com>
Date:   Thu, 16 Apr 2020 13:08:55 +0530
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Sorry Jan and others. Please ignore this patch.
I will resend a proper one after making sure it is tested via syzbot.

On 4/14/20 9:20 PM, Jan Kara wrote:
> 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@linux.ibm.com>
>> Reported-by: syzbot+77fa5bdb65cc39711820@syzkaller.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@suse.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
>>