linux-kernel - Re: [PATCH v4] string.h: Add str_has

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Message-ID: <20181222101244.7da017c9@vmware.local.home>
Date:   Sat, 22 Dec 2018 10:12:44 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joe Perches <joe@...ches.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Andreas Schwab <schwab@...ux-m68k.org>, kernel-team@....com
Subject: Re: [PATCH v4] string.h: Add str_has_prefix() helper function

On Sat, 22 Dec 2018 23:24:11 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> > No, because we don't know the length of str.
> > 
> > 
> > 	[ str = "h\0[bad memory]" ]
> > 
> > 
> > 	str_has_prefix(str, "TEST THIS BIG STRING AT FRONT")
> > 
> > 
> > If we use memcmp(), then we are testing way after str has ended, and
> > that can cause a memory fault.  
> 
> I don't know what's the bad memory causing memory fault but anyway
> memcpy() should stop at the NUL character first as it's different, no?

No, that's the difference between memcpy() and strncpy(), memcpy()
doesn't care about nul characters. It's copying memory not strings.

-- Steve