CVE request - kernel: DoS on x86_64

[Eugene Teo <eugeneteo () kernel sg>]

Reported by Mathias Krause. The problem seams to be located in
fs/binfmt_elf.c:load_elf_binary(). It calls SET_PERSONALITY() prior 
checking that the ELF interpreter is available. This in turn makes the 
previously 32 bit process a 64 bit one which would be fine if execve() 
would succeed. But after the SET_PERSONALITY() the open_exec() call 
fails (because it cannot find the interpreter) and execve() almost 
instantly returns with an error. If you now look at /proc/PID/maps 
you'll see, that it has the vsyscall page mapped which shouldn't be. But 
the process is not dead yet, it's still running. By now generating a 
segmentation fault and in turn trying to generate a core dump the
kernel just dies.

Steps to Reproduce:
1. Enable core dumps
2. Start an 32 bit program that tries to execve() an 64 bit program
3. The 64 bit program cannot be started by the kernel because it can't 
find the interpreter, i.e. execve returns with an error
4. Generate a segmentation fault
5. panic

Upstream commit:
http://git.kernel.org/linus/221af7f87b97431e3ee21ce4b0e77d5411cf1549

References:
http://marc.info/?t=126466700200002&r=1&w=2
https://bugzilla.redhat.com/show_bug.cgi?id=560547

Thanks, Eugene