On Tue, Dec 4, 2018 at 11:33 AM Linus Torvalds <torva...@linux-foundation.org> wrote: > > Looking at this, I'm agreeing that ot would be better to just try to > narrow down the cred_guard_mutex use a lot.
Ho humm. This is a crazy idea, but I don't see why it wouldn't work. How about we: - stop holding on to cred_guard_mutex entirely in the exec path and instead just do: - prepare_bprm_creds takes a ref to our old creds, and saves it off in the bprm - security_bprm_{committing,committed}_creds() can do it's "is this a valid transition" using the saved-off old creds instead of the current creds because honestly, the *only* reason we hold on to that lock is for the insane and not really interesting case of "somebody tried to use ptrace to change the creds in-flight during the exec". Or maybe we could just add a task state flag that says "in exec, you can't modify the creds in this window, because we're about to switch to new creds". Again, no *normal* situation will even notice or care, I think. We hold the cred lock purely to make sure that the sequence from prepare_exec_creds -> install_exec_creds is "atomic" wrt credentials, and it already is for all the normal cases since this is all inside a single execve system call. Linus