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Wed, 04 Sep 2019 15:15:40 -0700 (PDT) Subject: Re: [PATCH iproute2-next] bpf: fix snprintf truncation warning To: Andrea Claudi , netdev@vger.kernel.org Cc: stephen@networkplumber.org, dsahern@kernel.org References: <12a9cb8d91e41a08466141d4bb8ee659487d01df.1567611976.git.aclaudi@redhat.com> From: David Ahern Message-ID: <83242eb4-6304-0fcf-2d2a-6ef4de464e81@gmail.com> Date: Wed, 4 Sep 2019 16:15:39 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <12a9cb8d91e41a08466141d4bb8ee659487d01df.1567611976.git.aclaudi@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 9/4/19 9:50 AM, Andrea Claudi wrote: > gcc v9.2.1 produces the following warning compiling iproute2: > > bpf.c: In function ‘bpf_get_work_dir’: > bpf.c:784:49: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=] > 784 | snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt); > | ^ > bpf.c:784:2: note: ‘snprintf’ output between 2 and 4097 bytes into a destination of size 4096 > 784 | snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > Fix it extending bpf_wrk_dir size by 1 byte for the extra "/" char. > > Signed-off-by: Andrea Claudi > --- > lib/bpf.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/bpf.c b/lib/bpf.c > index 7d2a322ffbaec..95de7894a93ce 100644 > --- a/lib/bpf.c > +++ b/lib/bpf.c > @@ -742,7 +742,7 @@ static int bpf_gen_hierarchy(const char *base) > static const char *bpf_get_work_dir(enum bpf_prog_type type) > { > static char bpf_tmp[PATH_MAX] = BPF_DIR_MNT; > - static char bpf_wrk_dir[PATH_MAX]; > + static char bpf_wrk_dir[PATH_MAX + 1]; > static const char *mnt; > static bool bpf_mnt_cached; > const char *mnt_env = getenv(BPF_ENV_MNT); > PATH_MAX is meant to be the max length for a filesystem path including the null terminator, so I think it would be better to change the snprintf to 'sizeof(bpf_wrk_dir) - 1'.