linux-kernel - Re: [for-next][PATCH 23/24] string.h: Add strncmp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <077eeb8b09baebe78822819b5f15d671b738a2b2.camel@perches.com>
Date:   Fri, 21 Dec 2018 12:46:47 -0800
From:   Joe Perches <joe@...ches.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper
 macro

On Fri, 2018-12-21 at 15:35 -0500, Steven Rostedt wrote:
> At first I thought this would have issues, but with a slight change...
> 
> #define have_prefix(str, prefix) ({ \
> 	const char *__pfx = (const char *)prefix; \
> 
> 
> And the rest the same, it appears to work.
> 
> Need the cast because if for some reason someone passed in something
> like "const unsigned char" then it wouldn't work. But that's just a nit.
> 
> So something like this then?
> 
> -- Steve
> 
> diff --git a/include/linux/string.h b/include/linux/string.h
[]
> @@ -14,6 +14,28 @@ extern void *memdup_user(const void __user *, size_t);
>  extern void *vmemdup_user(const void __user *, size_t);
>  extern void *memdup_user_nul(const void __user *, size_t);
>  
> +/**
> + * have_prefix - Test if a string has a given prefix

There is a naming mismatch of have/has here
and has_prefix is probably too generic a name.

How about str_has_prefix?

> + * @str: The string to test
> + * @prefix: The string to see if @str starts with
> + *
> + * A common way to test a prefix of a string is to do:
> + *  strncmp(str, prefix, sizeof(prefix) - 1)
> + *
> + * But this can lead to bugs due to typos, or if prefix is a pointer
> + * and not a constant. Instead use has_prefix().
> + *
> + * Returns: 0 if @str does not start with @prefix
> +         strlen(@prefix) if @str does start with @prefix
> + */
> +#define has_prefix(str, prefix)						\
> +	({								\
> +		const char *____prefix____ = (const char *)(prefix);	\
> +		int ____len____ = strlen(____prefix____);		\
> +		strncmp(str, ____prefix____, ____len____) == 0 ?	\
> +			____len____ : 0;				\
> +	}) 

I think all the underscores are unnecessary and confusing.