Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 5.16 002/200] btrfs: fix too long loop when defragging a 1 byte file | Date | Mon, 31 Jan 2022 11:54:25 +0100 |
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From: Filipe Manana <fdmanana@suse.com>
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@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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- 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;
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