A use after free vulnerability was found in kernel which allows privilege escalation for users with a local account on the system. When a program was loaded with a bpf program an attacker could exploit this to gain root privileges by an unprivileged user.


When bpf(BPF_PROG_LOAD, ...) was invoked with a BPF program whose bytecode references a non-map file descriptor as a map file descriptor, the error handling code called fdput() twice instead of once (in __bpf_map_get() and in replace_map_fd_with_map_ptr()). If the file descriptor table of the current task is shared, this causes f_count to be decremented too much, allowing the struct file to be freed while it is still in use (use-after-free).

Bug was introduced in 0246e64d9a5f and is exploitable since 1be7f75d1668 without the need for CAP_SYS_ADMIN capability.

Upstream patch:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=8358b02bf67d3a5d8a825070e1aa73f25fb2e4c7

Original report:

https://bugs.chromium.org/p/project-zero/issues/detail?id=808

CVE request:

http://seclists.org/oss-sec/2016/q2/263