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

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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@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





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