linux-kernel - [PATCH 4.9 15/36] f2fs: fix a dead loop in f2fs

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Date:   Mon, 14 May 2018 08:48:49 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Wei Fang <fangwei1@...wei.com>,
        Chao Yu <yuchao0@...wei.com>, Jaegeuk Kim <jaegeuk@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH 4.9 15/36] f2fs: fix a dead loop in f2fs_fiemap()

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

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

From: Wei Fang <fangwei1@...wei.com>

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@...wei.com>
Acked-by: Chao Yu <yuchao0@...wei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -844,7 +844,7 @@ 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;
 }