| Message ID | tencent_EE3E19F80ACD66955D26A878BC768CFA210A@qq.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [bpf-next] selftests/bpf: Fix strncpy() fortify warning | expand |
On Thu, Oct 27, 2022 at 4:34 AM Rong Tao <rtoax@foxmail.com> wrote: > > From: Rong Tao <rongtao@cestc.cn> > > Compile samples/bpf, error: > $ cd samples/bpf > $ make > ... > In function ‘__enable_controllers’: > samples/bpf/../../tools/testing/selftests/bpf/cgroup_helpers.c:80:17: warning: ‘strncpy’ specified bound 4097 equals destination size [-Wstringop-truncation] > 80 | strncpy(enable, controllers, sizeof(enable)); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > Signed-off-by: Rong Tao <rongtao@cestc.cn> > --- > tools/testing/selftests/bpf/cgroup_helpers.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c > index e914cc45b766..a70e873b267e 100644 > --- a/tools/testing/selftests/bpf/cgroup_helpers.c > +++ b/tools/testing/selftests/bpf/cgroup_helpers.c > @@ -77,7 +77,7 @@ static int __enable_controllers(const char *cgroup_path, const char *controllers > enable[len] = 0; > close(fd); > } else { > - strncpy(enable, controllers, sizeof(enable)); > + strncpy(enable, controllers, sizeof(enable) - 1); enable is not initialized, so we might end up with non-zero-terminated string. Let's enable[0] = '\0'; at the beginning and then strncat() here? > } > > snprintf(path, sizeof(path), "%s/cgroup.subtree_control", cgroup_path); > -- > 2.31.1 >
Thanks for your reply, `enable[0] = '\0';` at the beginning and then
strncat() still has the same compile warning
--- a/tools/testing/selftests/bpf/cgroup_helpers.c
+++ b/tools/testing/selftests/bpf/cgroup_helpers.c
@@ -77,7 +77,8 @@ static int __enable_controllers(const char *cgroup_path, const char *controllers
enable[len] = 0;
close(fd);
} else {
- strncpy(enable, controllers, sizeof(enable));
+ enable[0] = '\0';
+ strncat(enable, controllers, sizeof(enable));
}
In function ‘__enable_controllers’:
tools/testing/selftests/bpf/cgroup_helpers.c:81:17: warning: ‘strncat’ specified bound 4097 equals destination size [-Wstringop-truncation]
81 | strncat(enable, controllers, sizeof(enable));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/testing/selftests/bpf/cgroup_helpers.c:81:17: warning: ‘strncat’ specified bound 4097 equals destination size [-Wstringop-overflow=]
So, i think just add '-1' for strncpy() is a good way.
On Thu, Oct 27, 2022 at 5:26 PM Rong Tao <rtoax@foxmail.com> wrote: > > Thanks for your reply, `enable[0] = '\0';` at the beginning and then > strncat() still has the same compile warning > > --- a/tools/testing/selftests/bpf/cgroup_helpers.c > +++ b/tools/testing/selftests/bpf/cgroup_helpers.c > @@ -77,7 +77,8 @@ static int __enable_controllers(const char *cgroup_path, const char *controllers > enable[len] = 0; > close(fd); > } else { > - strncpy(enable, controllers, sizeof(enable)); > + enable[0] = '\0'; > + strncat(enable, controllers, sizeof(enable)); > } > > In function ‘__enable_controllers’: > tools/testing/selftests/bpf/cgroup_helpers.c:81:17: warning: ‘strncat’ specified bound 4097 equals destination size [-Wstringop-truncation] > 81 | strncat(enable, controllers, sizeof(enable)); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > tools/testing/selftests/bpf/cgroup_helpers.c:81:17: warning: ‘strncat’ specified bound 4097 equals destination size [-Wstringop-overflow=] > > So, i think just add '-1' for strncpy() is a good way. no, it's not, see my previous email about ending up with non-zero-terminated C string. check strncat() API, it leaves the dst string zero terminated, and yes, you need -1 for strncat as well, your compiler is right
diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c index e914cc45b766..a70e873b267e 100644 --- a/tools/testing/selftests/bpf/cgroup_helpers.c +++ b/tools/testing/selftests/bpf/cgroup_helpers.c @@ -77,7 +77,7 @@ static int __enable_controllers(const char *cgroup_path, const char *controllers enable[len] = 0; close(fd); } else { - strncpy(enable, controllers, sizeof(enable)); + strncpy(enable, controllers, sizeof(enable) - 1); } snprintf(path, sizeof(path), "%s/cgroup.subtree_control", cgroup_path);