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* [PATCH nf-next] netfilter: bpf: Pass string literal as format argument of request_module()
@ 2024-10-18  9:42 Simon Horman
  2024-10-18  9:44 ` Florian Westphal
  2024-10-18 10:35 ` Toke Høiland-Jørgensen
  0 siblings, 2 replies; 5+ messages in thread
From: Simon Horman @ 2024-10-18  9:42 UTC (permalink / raw)
  To: Pablo Neira Ayuso, Jozsef Kadlecsik
  Cc: David S. Miller, Eric Dumazet, Jakub Kicinski, Paolo Abeni,
	Nathan Chancellor, Nick Desaulniers, Bill Wendling, Justin Stitt,
	netfilter-devel, coreteam, netdev, bpf, llvm

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.

No functional change intended.
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 5257d5e7eb09..6b9c9d71906d 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -42,7 +42,7 @@ 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);
 


^ permalink raw reply related	[flat|nested] 5+ messages in thread
* [PATCH nf-next] netfilter: bpf: Pass string literal as format argument of request_module()
@ 2024-11-11 14:47 Simon Horman
  2024-11-12 11:36 ` Pablo Neira Ayuso
  0 siblings, 1 reply; 5+ messages in thread
From: Simon Horman @ 2024-11-11 14:47 UTC (permalink / raw)
  To: Pablo Neira Ayuso, Jozsef Kadlecsik
  Cc: David S. Miller, Eric Dumazet, Jakub Kicinski, Paolo Abeni,
	Nathan Chancellor, Nick Desaulniers, Bill Wendling, Justin Stitt,
	netfilter-devel, coreteam, netdev, linux-kernel, bpf, llvm

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);
 


^ permalink raw reply related	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-11-12 11:36 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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2024-10-18  9:42 [PATCH nf-next] netfilter: bpf: Pass string literal as format argument of request_module() Simon Horman
2024-10-18  9:44 ` Florian Westphal
2024-10-18 10:35 ` Toke Høiland-Jørgensen
  -- strict thread matches above, loose matches on Subject: below --
2024-11-11 14:47 Simon Horman
2024-11-12 11:36 ` Pablo Neira Ayuso

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