From: Filipe Manana <fdmanana@xxxxxxxx>
commit 6b34cd8e175bfbf4f3f01b6d19eae18245e1a8cc upstream.
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@xxxxxxxxxxx>
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@xxxxxxxxxxx/
CC: stable@xxxxxxxxxxxxxxx # 5.16
Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/ioctl.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1492,12 +1492,16 @@ int btrfs_defrag_file(struct inode *inod
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
@@ -1510,10 +1514,6 @@ int btrfs_defrag_file(struct inode *inod
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;
