Kees Cook <keescook@xxxxxxxxxxxx> writes: > On Wed, Jan 26, 2022 at 08:08:14PM +0000, Matthew Wilcox wrote: >> On Wed, Jan 26, 2022 at 11:58:39AM -0800, Kees Cook wrote: >> > We can't mutate argc; it'll turn at least some userspace into an >> > infinite loop: >> > https://sources.debian.org/src/valgrind/1:3.18.1-1/none/tests/execve.c/?hl=22#L22 >> >> How does that become an infinite loop? We obviously wouldn't mutate >> argc in the caller, just the callee. > > Oh, sorry, I misread. It's using /bin/true, not argv[0] (another bit of > code I found was using argv[0]). Yeah, {"", NULL} could work. > >> Also, there's a version of this where we only mutate argc if we're >> executing a setuid program, which would remove the privilege >> escalation part of things. > > True; though I'd like to keep the logic as non-specialized as possible. > I don't like making stuff conditional on privilege boundaries if we can > make it always happen. Which I think means turning the argc == 0 case into { "", NULL }. I think we can always do that, and it is already valid in userspace. The only case I can imagine breaking would be an explicitly testing for argc == 0 and behaving completely differently if that is passed to the program. Eric
