Re: [PATCH v5] Added PR_SET_PROCTITLE_AREA option for prctl()

On Mon, Nov 9, 2009 at 5:47 PM, Andrew Morton [off-list ref] wrote:

What happens if userspace unmaps the memory after telling the kernel to
use it?

Will processes which try to read the command line get an error reading
/proc?  If so, do all the commandline-reading programs in the world
handle this in an appropriate fashion?

This case can already occur in the current code; the userspace process
would have to munmap() the top of its stack, but it certainly can do
so if it tries. In any case, access_process_vm() then returns 0
because of the fault, and thus /proc/pid/cmdline is seen to have zero
length. Since a zero-length /proc/pid/cmdline occurs with kernel
threads as well, we know this isn't a problem.