Re: [RFC 1/1] ext4: Fix overflow case for map.m_len in ext4_iomap_begin_*

[Ritesh Harjani <riteshh@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
> > Reported-by: syzbot+77fa5bdb65cc39711820@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Fixes: d3b6f23f7167 ("ext4: move ext4_fiemap to use iomap framework")
>
> The patch looks good to me. You can add:
>
> Reviewed-by: Jan Kara <jack@xxxxxxx>
>
> 								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