Local root exploit for CVE-2014-0038

Bug:

The X86_X32 recvmmsg syscall does not properly sanitize the timeout pointer passed from userspace.

Exploit primitive:

Pass a pointer to a kernel address as timeout for recvmmsg, if the original byte at that address is known it can be overwritten with known data. If the least significant byte is 0xff, waiting 255 seconds will turn it into a 0x00.

Restrictions:

The first long at the passed address (tv_sec) has to be positive and the second long (tv_nsec) has to be smaller than 1000000000.

Overview:

Target the release function pointer of the ptmx_fops structure located in non initialized (and thus writable) kernel memory. Zero out the three most significant bytes and thus turn it into a pointer to an address mappable in user space. The release pointer is used as it is followed by 16 0x00 bytes (so the tv_nsec is valid). Open /dev/ptmx, close it and enjoy.

Not very beautiful but should be fairly reliable if symbols can be resolved.

Tested on Ubuntu 13.10

Run:

Retrieve addresses from /proc/kallsyms and run the exploit:

./build.sh && ./timeoutpwn

If you would like to build the binary for a remote server, try this:

ssh user@host 'cat /proc/kallsyms' > syms.txt
CFLAGS=-static ./build.sh syms.txt
scp timeoutpwn user@host:
...

If ptmx_fops cannot be found in kallsyms, try extracting it from the vmlinux as provided with the headers package (linux-headers on Arch Linux):