linux-kernel - Re: [PATCH] kdb: Fix bound check compiler warning

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Date:   Mon, 13 May 2019 08:44:44 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Wenlin Kang <wenlin.kang@...driver.com>
Cc:     jason.wessel@...driver.com, prarit@...hat.com,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kdb: Fix bound check compiler warning

On Mon, May 13, 2019 at 11:39:47AM +0800, Wenlin Kang wrote:
> On 5/12/19 5:00 PM, Daniel Thompson wrote:
> > On Thu, May 09, 2019 at 10:56:03AM +0800, Wenlin Kang wrote:
> > > On 5/8/19 4:16 PM, Daniel Thompson wrote:
> > > > On Wed, May 08, 2019 at 09:52:39AM +0800, Wenlin Kang wrote:
> > > > > The strncpy() function may leave the destination string buffer
> > > > > unterminated, better use strlcpy() instead.
> > > > > 
> > > > > This fixes the following warning with gcc 8.2:
> > > > > 
> > > > > kernel/debug/kdb/kdb_io.c: In function 'kdb_getstr':
> > > > > kernel/debug/kdb/kdb_io.c:449:3: warning: 'strncpy' specified bound 256 equals destination size [-Wstringop-truncation]
> > > > >      strncpy(kdb_prompt_str, prompt, CMD_BUFLEN);
> > > > >      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > 
> > > > > Signed-off-by: Wenlin Kang <wenlin.kang@...driver.com>
> > > > > ---
> > > > >    kernel/debug/kdb/kdb_io.c | 2 +-
> > > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> > > > > index 6a4b414..7fd4513 100644
> > > > > --- a/kernel/debug/kdb/kdb_io.c
> > > > > +++ b/kernel/debug/kdb/kdb_io.c
> > > > > @@ -446,7 +446,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
> > > > >    char *kdb_getstr(char *buffer, size_t bufsize, const char *prompt)
> > > > >    {
> > > > >    	if (prompt && kdb_prompt_str != prompt)
> > > > > -		strncpy(kdb_prompt_str, prompt, CMD_BUFLEN);
> > > > > +		strlcpy(kdb_prompt_str, prompt, CMD_BUFLEN);
> > > > Shouldn't that be strscpy?
> > > 
> > > Hi Daniel
> > > 
> > > I thought about strscpy, but I think strlcpy is better, because it only copy
> > > the real number of characters if src string less than that size.
> > Sorry, I'm confused by this. What behavior does strscpy() have that you
> > consider undesirable in this case?
> 
> 
> Hi Daniel
> 
> I checked strscpy() again, and think either is fine to me, if you think
> strscpy() is better, I can change it to this, and send v2, thanks for your
> review.

I think strscpy() is better.


Daniel.

> 
> 
> > 
> > Daniel.
> > 
> 
> -- 
> Thanks,
> Wenlin Kang
>