[PATCH nf-next] netfilter: bpf: Pass string literal as format argument of request_module()

[PATCH nf-next] netfilter: bpf: Pass string literal as format argument of request_module()

[Simon Horman]

Both gcc-14 and clang-18 report that passing a non-string literal as the
format argument of request_module() is potentially insecure.

E.g. clang-18 says:

.../nf_bpf_link.c:46:24: warning: format string is not a string literal (potentially insecure) [-Wformat-security]
   46 |                 err = request_module(mod);
      |                                      ^~~
.../kmod.h:25:55: note: expanded from macro 'request_module'
   25 | #define request_module(mod...) __request_module(true, mod)
      |                                                       ^~~
.../nf_bpf_link.c:46:24: note: treat the string as an argument to avoid this
   46 |                 err = request_module(mod);
      |                                      ^
      |                                      "%s",
.../kmod.h:25:55: note: expanded from macro 'request_module'
   25 | #define request_module(mod...) __request_module(true, mod)
      |                                                       ^

It is always the case where the contents of mod is safe to pass as the
format argument. That is, in my understanding, it never contains any
format escape sequences.

But, it seems better to be safe than sorry. And, as a bonus, compiler
output becomes less verbose by addressing this issue as suggested by
clang-18.

Compile tested only.

Signed-off-by: Simon Horman <horms@kernel.org>
---
 net/netfilter/nf_bpf_link.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
index 3d64a4511fcf..06b084844700 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -43,7 +43,7 @@ get_proto_defrag_hook(struct bpf_nf_link *link,
 	hook = rcu_dereference(*ptr_global_hook);
 	if (!hook) {
 		rcu_read_unlock();
-		err = request_module(mod);
+		err = request_module("%s", mod);
 		if (err)
 			return ERR_PTR(err < 0 ? err : -EINVAL);
 

Re: [PATCH nf-next] netfilter: bpf: Pass string literal as format argument of request_module()

[Pablo Neira Ayuso]

On Mon, Nov 11, 2024 at 02:47:51PM +0000, Simon Horman wrote:
> Both gcc-14 and clang-18 report that passing a non-string literal as the
> format argument of request_module() is potentially insecure.

Applied to nf-next