From: Stafford Horne Subject: Re: [PATCH v2 2/2] kobject: Fix -Wstringop-truncation warning Date: Mon, 25 Jun 2018 22:24:45 +0900 Message-ID: <20180625132445.GI24595@lianli.shorne-pla.net> References: <20180625124538.21051-1-shorne@gmail.com> <20180625124538.21051-3-shorne@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: LKML , Greg KH , arnd@arndb.de, Eric Biggers , linux-crypto@vger.kernel.org To: Christophe LEROY Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On Mon, Jun 25, 2018 at 02:57:13PM +0200, Christophe LEROY wrote: > > > Le 25/06/2018 à 14:45, Stafford Horne a écrit : > > When compiling with GCC 9.0.0 I am seeing the following warning: > > > > In function ‘fill_kobj_path’, > > inlined from ‘kobject_get_path’ at lib/kobject.c:155:2: > > lib/kobject.c:128:3: warning: ‘strncpy’ output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation] > > strncpy(path + length, kobject_name(parent), cur); > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > lib/kobject.c: In function ‘kobject_get_path’: > > lib/kobject.c:125:13: note: length computed here > > int cur = strlen(kobject_name(parent)); > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > This is not really an issue since the buffer we are writing to is > > pre-zero'd and we have already allocated the buffer based on the > > calculated strlen size and accounted for the terminating '\0'. > > Just use memcpy() instead. > > If we are already sure the destination is big enough, why not just do a > strcpy() and drop the 'cur = strlen()' ? Hi Christophe, Here were are writing multiple strings into a buffer from back to front. We are copying exactly strlen() bytes at a time to avoid the nul terminator being copied into the buffer. I don't doubt we could use strcpy() but I was trying to keep the change small. -Stafford > > > > Cc: Greg Kroah-Hartman > > Cc: Arnd Bergmann > > Cc: Eric Biggers > > Signed-off-by: Stafford Horne > > --- > > lib/kobject.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/lib/kobject.c b/lib/kobject.c > > index 18989b5b3b56..e876957743c8 100644 > > --- a/lib/kobject.c > > +++ b/lib/kobject.c > > @@ -125,7 +125,7 @@ static void fill_kobj_path(struct kobject *kobj, char *path, int length) > > int cur = strlen(kobject_name(parent)); > > /* back up enough to print this name with '/' */ > > length -= cur; > > - strncpy(path + length, kobject_name(parent), cur); > > + memcpy(path + length, kobject_name(parent), cur); > > *(path + --length) = '/'; > > } > >