[PATCH 4.4 42/56] f2fs: fix a dead loop in f2fs_fiemap()

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wei Fang <fangwei1@xxxxxxxxxx>

commit b86e33075ed1909d8002745b56ecf73b833db143 upstream.

A dead loop can be triggered in f2fs_fiemap() using the test case
as below:

	...
	fd = open();
	fallocate(fd, 0, 0, 4294967296);
	ioctl(fd, FS_IOC_FIEMAP, fiemap_buf);
	...

It's caused by an overflow in __get_data_block():
	...
	bh->b_size = map.m_len << inode->i_blkbits;
	...
map.m_len is an unsigned int, and bh->b_size is a size_t which is 64 bits
on 64 bits archtecture, type conversion from an unsigned int to a size_t
will result in an overflow.

In the above-mentioned case, bh->b_size will be zero, and f2fs_fiemap()
will call get_data_block() at block 0 again an again.

Fix this by adding a force conversion before left shift.

Signed-off-by: Wei Fang <fangwei1@xxxxxxxxxx>
Acked-by: Chao Yu <yuchao0@xxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/f2fs/data.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -721,7 +721,7 @@ static int __get_data_block(struct inode
 	if (!ret) {
 		map_bh(bh, inode->i_sb, map.m_pblk);
 		bh->b_state = (bh->b_state & ~F2FS_MAP_FLAGS) | map.m_flags;
-		bh->b_size = map.m_len << inode->i_blkbits;
+		bh->b_size = (u64)map.m_len << inode->i_blkbits;
 	}
 	return ret;
 }