[PATCH] Btrfs: fix inode eviction infinite loop after extent_same ioctl

[PATCH] Btrfs: fix inode eviction infinite loop after extent_same ioctl

[Filipe Manana]

If we pass a length of 0 to the extent_same ioctl, we end up locking an
extent range with a start offset greater then its end offset (if the
destination file's offset is greater than zero). This results in a warning
from extent_io.c:insert_state through the following call chain:

  btrfs_extent_same()
    btrfs_double_lock()
      lock_extent_range()
        lock_extent(inode->io_tree, offset, offset + len - 1)
          lock_extent_bits()
            __set_extent_bit()
              insert_state()
                --> WARN_ON(end < start)

This leads to an infinite loop when evicting the inode. This is the same
problem that my previous patch titled
"Btrfs: fix inode eviction infinite loop after cloning into it" addressed
but for the extent_same ioctl instead of the clone ioctl.

CC: <stable@vger.kernel.org>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/ioctl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 4c32350..09a566a 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2897,6 +2897,9 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 len,
 	if (src == dst)
 		return -EINVAL;
 
+	if (len == 0)
+		return 0;
+
 	btrfs_double_lock(src, loff, dst, dst_loff, len);
 
 	ret = extent_same_check_offsets(src, loff, len);
-- 
2.1.3

Re: [PATCH] Btrfs: fix inode eviction infinite loop after extent_same ioctl

[Omar Sandoval]

On Mon, Mar 30, 2015 at 06:26:47PM +0100, Filipe Manana wrote:
> If we pass a length of 0 to the extent_same ioctl, we end up locking an
> extent range with a start offset greater then its end offset (if the
> destination file's offset is greater than zero). This results in a warning
> from extent_io.c:insert_state through the following call chain:
> 
>   btrfs_extent_same()
>     btrfs_double_lock()
>       lock_extent_range()
>         lock_extent(inode->io_tree, offset, offset + len - 1)
>           lock_extent_bits()
>             __set_extent_bit()
>               insert_state()
>                 --> WARN_ON(end < start)
> 
> This leads to an infinite loop when evicting the inode. This is the same
> problem that my previous patch titled
> "Btrfs: fix inode eviction infinite loop after cloning into it" addressed
> but for the extent_same ioctl instead of the clone ioctl.
> 
> CC: <stable@vger.kernel.org>
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Omar Sandoval <osandov@osandov.com>

Reproduced with https://github.com/markfasheh/duperemove/blob/master/btrfs-extent-same.c

./btrfs-extent-same 0 foo 4096 bar 4096

-- 
Omar