CVE 2010-1636
The btrfs_ioctl_clone function in fs/btrfs/ioctl.c in the btrfs functionality in the Linux kernel 2.6.29 through 2.6.32, and possibly other versions, does not ensure that a cloned file descriptor has been opened for reading, which allows local users to read sensitive information from a write-only file descriptor.
See the 
CVE page on Mitre.org
for more details.
