linux-kernel - Re: [PATCH] exec: refactor an invalid executable check to use isprint

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Message-ID: <20241115170447.GX3387508@ZenIV>
Date: Fri, 15 Nov 2024 17:04:47 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Nir Lichtman <nir@...htman.org>
Cc: brauner@...nel.org, jack@...e.cz, ebiederm@...ssion.com,
	kees@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exec: refactor an invalid executable check to use isprint

On Fri, Nov 15, 2024 at 04:53:51PM +0000, Nir Lichtman wrote:
> Remove private printable macro that is defined in exec.c and migrate to
> using the public isprint macro instead


> -#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))

> -		if (printable(bprm->buf[0]) && printable(bprm->buf[1]) &&
> -		    printable(bprm->buf[2]) && printable(bprm->buf[3]))
> +		if (isprint(bprm->buf[0]) && isprint(bprm->buf[1]) &&
> +		    isprint(bprm->buf[2]) && isprint(bprm->buf[3]))

RTFM(isprint).  Or run a trivial loop and check what it does, for that
matter.

isprint('\t') is false.  So's isprint('\n').