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Date: Wed, 26 Jan 2022 14:31:16 -0600 From: "Eric W. Biederman" <ebiederm@...ssion.com> To: Kees Cook <keescook@...omium.org> Cc: Matthew Wilcox <willy@...radead.org>, Jann Horn <jannh@...gle.com>, Ariadne Conill <ariadne@...eferenced.org>, Michael Kerrisk <mtk.manpages@...il.com>, Christian Brauner <brauner@...nel.org>, Rich Felker <dalias@...c.org>, Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org, stable@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] fs/binfmt_elf: Add padding NULL when argc == 0 Kees Cook <keescook@...omium.org> 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
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