Reported to secalert@redhat.com by Ilja van Sprundel, a race condition in execve
affecting x86_64 and ia64 which exists because kmalloc() or get_user() can
block, and hence another thread can change the argv and envp pointers, causing a
bufferoverflow (also on SMP without blocking)

          na = nargs(argv, NULL);
 ...      ne = nargs(envp, NULL);
 ...      len = (na + ne + 2) * sizeof(*av);
 ...      av = kmalloc(len, GFP_KERNEL);
 ...      r = nargs(argv, av);
 ...      r = nargs(envp, ae);

"the nargs() function is used to first count the amount of argv and
envp pointers, next a kmalloc() is done, and then nargs() is called again to
copy the argv and envp pointer into this newly allocated memory.        the race
condition exists because kmalloc() or get_user() can block, and hence another
thread can change the argv and envp pointers, causing a buffer overflow."

Currently embargoed