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

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Message-ID: <20190512090003.de52davu55rrg7kn@wychelm.lan>
Date:   Sun, 12 May 2019 10:00:03 +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 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?


Daniel.