linux-kernel - Re: [PATCH 1/4] exec: Change uselib(2) IS

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Message-ID: <20200518130251.zih2s32q2rxhxg6f@wittgenstein>
Date:   Mon, 18 May 2020 15:02:51 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
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 1/4] exec: Change uselib(2) IS_SREG() failure to EACCES

On Sun, May 17, 2020 at 10:54:54PM -0700, Kees Cook wrote:
> Change uselib(2)' S_ISREG() error return to EACCES instead of EINVAL so
> the behavior matches execve(2), and the seemingly documented value.
> The "not a regular file" failure mode of execve(2) is explicitly
> documented[1], but it is not mentioned in uselib(2)[2] which does,
> however, say that open(2) and mmap(2) errors may apply. The documentation
> for open(2) does not include a "not a regular file" error[3], but mmap(2)
> does[4], and it is EACCES.
> 
> [1] http://man7.org/linux/man-pages/man2/execve.2.html#ERRORS
> [2] http://man7.org/linux/man-pages/man2/uselib.2.html#ERRORS
> [3] http://man7.org/linux/man-pages/man2/open.2.html#ERRORS
> [4] http://man7.org/linux/man-pages/man2/mmap.2.html#ERRORS
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

This is all extremely weird.
uselib has been deprected since forever basically which makes me doubt
this matters much but:
Acked-by: Christian Brauner <christian.brauner@...ntu.com>

Also - gulp (puts on flame proof suit) - may I suggest we check if there
are any distros out there that still set CONFIG_USELIB=y and if not do
what we did with the sysctl syscall and remove it? If someone yells we
can always backpaddle...

Christian