[PATCH 4.5 090/101] Btrfs: fix extent_same allowing destination offset beyond i_size

Greg Kroah-Hartman
2016-05-17T01:32:24Z

From: Filipe Manana <fdmanana@suse.com>

commit f4dfe6871006c62abdccc77b2818b11f376e98e2 upstream.

When using the same file as the source and destination for a dedup
(extent_same ioctl) operation we were allowing it to dedup to a
destination offset beyond the file's size, which doesn't make sense and
it's not allowed for the case where the source and destination files are
not the same file. This made de deduplication operation successful only
when the source range corresponded to a hole, a prealloc extent or an
extent with all bytes having a value of 0x00. This was also leaving a
file hole (between i_size and destination offset) without the
corresponding file extent items, which can be reproduced with the
following steps for example:

$ mkfs.btrfs -f /dev/sdi
$ mount /dev/sdi /mnt/sdi

$ xfs_io -f -c "pwrite -S 0xab 304457 404990" /mnt/sdi/foobar
wrote 404990/404990 bytes at offset 304457
395 KiB, 99 ops; 0.0000 sec (31.150 MiB/sec and 7984.5149 ops/sec)

$ /git/hub/duperemove/btrfs-extent-same 24576 /mnt/sdi/foobar 28672 /mnt/sdi/foobar 929792
Deduping 2 total files
(28672, 24576): /mnt/sdi/foobar
(929792, 24576): /mnt/sdi/foobar
1 files asked to be deduped
i: 0, status: 0, bytes_deduped: 24576
24576 total bytes deduped in this operation

$ umount /mnt/sdi
$ btrfsck /dev/sdi
Checking filesystem on /dev/sdi
UUID: 98c528aa-0833-427d-9403-b98032ffbf9d
checking extents
checking free space cache
checking fs roots
root 5 inode 257 errors 100, file extent discount
Found file extent holes:
start: 712704, len: 217088
found 540673 bytes used err is 1
total csum bytes: 400
total tree bytes: 131072
total fs tree bytes: 32768
total extent tree bytes: 16384
btree space waste bytes: 123675
file data blocks allocated: 671744
referenced 671744
btrfs-progs v4.2.3

So fix this by not allowing the destination to go beyond the file's size,
just as we do for the same where the source and destination files are not
the same.

A test for xfstests follows.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/ioctl.c | 3 +++
1 file changed, 3 insertions(+)

--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3069,6 +3069,9 @@ static int btrfs_extent_same(struct inod
ret = extent_same_check_offsets(src, loff, &len, olen);
if (ret)
goto out_unlock;
+ ret = extent_same_check_offsets(src, dst_loff, &len, olen);
+ if (ret)
+ goto out_unlock;

/*
* Single inode case wants the same checks, except we