diff options
| author | Filipe Manana | 2022-01-17 16:28:29 +0000 |
|---|---|---|
| committer | David Sterba | 2022-01-19 18:16:34 +0100 |
| commit | 6b34cd8e175bfbf4f3f01b6d19eae18245e1a8cc (patch) | |
| tree | b519456954c8af3f842d9e3cd7e653908ff044b4 | |
| parent | 36c86a9e1be3b29f9f075a946df55dfe1d818019 (diff) | |
btrfs: fix too long loop when defragging a 1 byte file
When attempting to defrag a file with a single byte, we can end up in a
too long loop, which is nearly infinite because at btrfs_defrag_file()
we end up with the variable last_byte assigned with a value of
18446744073709551615 (which is (u64)-1). The problem comes from the fact
we end up doing:
last_byte = round_up(last_byte, fs_info->sectorsize) - 1;
So if last_byte was assigned 0, which is i_size - 1, we underflow and
end up with the value 18446744073709551615.
This is trivial to reproduce and the following script triggers it:
$ cat test.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
mkfs.btrfs -f $DEV
mount $DEV $MNT
echo -n "X" > $MNT/foobar
btrfs filesystem defragment $MNT/foobar
umount $MNT
So fix this by not decrementing last_byte by 1 before doing the sector
size round up. Also, to make it easier to follow, make the round up right
after computing last_byte.
Reported-by: Anthony Ruhier <aruhier@mailbox.org>
Fixes: 7b508037d4cac3 ("btrfs: defrag: use defrag_one_cluster() to implement btrfs_defrag_file()")
Link: https://lore.kernel.org/linux-btrfs/0a269612-e43f-da22-c5bc-b34b1b56ebe8@mailbox.org/
CC: stable@vger.kernel.org # 5.16
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
| -rw-r--r-- | fs/btrfs/ioctl.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index a5bd6926f7ff..6ad2bc2e5af3 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -1518,12 +1518,16 @@ int btrfs_defrag_file(struct inode *inode, struct file_ra_state *ra, if (range->start + range->len > range->start) { /* Got a specific range */ - last_byte = min(isize, range->start + range->len) - 1; + last_byte = min(isize, range->start + range->len); } else { /* Defrag until file end */ - last_byte = isize - 1; + last_byte = isize; } + /* Align the range */ + cur = round_down(range->start, fs_info->sectorsize); + last_byte = round_up(last_byte, fs_info->sectorsize) - 1; + /* * If we were not given a ra, allocate a readahead context. As * readahead is just an optimization, defrag will work without it so @@ -1536,10 +1540,6 @@ int btrfs_defrag_file(struct inode *inode, struct file_ra_state *ra, file_ra_state_init(ra, inode->i_mapping); } - /* Align the range */ - cur = round_down(range->start, fs_info->sectorsize); - last_byte = round_up(last_byte, fs_info->sectorsize) - 1; - while (cur < last_byte) { u64 cluster_end; |