Btrfs: fix checks in BTRFS_IOC_CLONE_RANGE

1.  The BTRFS_IOC_CLONE and BTRFS_IOC_CLONE_RANGE ioctls should check
whether the donor file is append-only before writing to it.

2.  The BTRFS_IOC_CLONE_RANGE ioctl appears to have an integer
overflow that allows a user to specify an out-of-bounds range to copy
from the source file (if off + len wraps around).  I haven't been able
to successfully exploit this, but I'd imagine that a clever attacker
could use this to read things he shouldn't.  Even if it's not
exploitable, it couldn't hurt to be safe.

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
cc: stable@kernel.org
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 2a8b3a7568ad..9254b3d58dbe 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1458,7 +1458,7 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
          */
 
         /* the destination must be opened for writing */
-        if (!(file->f_mode & FMODE_WRITE))
+        if (!(file->f_mode & FMODE_WRITE) || (file->f_flags & O_APPEND))
                 return -EINVAL;
 
         ret = mnt_want_write(file->f_path.mnt);
@@ -1511,7 +1511,7 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 
         /* determine range to clone */
         ret = -EINVAL;
-        if (off >= src->i_size || off + len > src->i_size)
+        if (off + len > src->i_size || off + len < off)
                 goto out_unlock;
         if (len == 0)
                 olen = len = src->i_size - off;