linux-kernel - Re: [PATCH 0/4] Relocate execve() sanity checks

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Message-ID: <87a724t153.fsf@x220.int.ebiederm.org>
Date:   Tue, 19 May 2020 10:06:32 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kees Cook <keescook@...omium.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Eric Biggers <ebiggers3@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] Relocate execve() sanity checks

Kees Cook <keescook@...omium.org> writes:

> Hi,
>
> While looking at the code paths for the proposed O_MAYEXEC flag, I saw
> some things that looked like they should be fixed up.
>
>   exec: Change uselib(2) IS_SREG() failure to EACCES
> 	This just regularizes the return code on uselib(2).
>
>   exec: Relocate S_ISREG() check
> 	This moves the S_ISREG() check even earlier than it was already.
>
>   exec: Relocate path_noexec() check
> 	This adds the path_noexec() check to the same place as the
> 	S_ISREG() check.
>
>   fs: Include FMODE_EXEC when converting flags to f_mode
> 	This seemed like an oversight, but I suspect there is some
> 	reason I couldn't find for why FMODE_EXEC doesn't get set in
> 	f_mode and just stays in f_flags.

So I took a look at this series.

I think the belt and suspenders approach of adding code in open and then
keeping it in exec and uselib is probably wrong.  My sense of the
situation is a belt and suspenders approach is more likely to be
confusing and result in people making mistakes when maintaining the code
than to actually be helpful.

Eric