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  1. Jan 20, 2022
    • Filipe Manana's avatar
      btrfs: fix too long loop when defragging a 1 byte file · 6b34cd8e
      Filipe Manana authored
      
      
      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: default avatarAnthony Ruhier <aruhier@mailbox.org>
      Fixes: 7b508037 ("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: default avatarQu Wenruo <wqu@suse.com>
      Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
      Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
      6b34cd8e
  2. Jan 07, 2022