From: Paul Chaignon <paul.chaignon@gmail.com>
Date: Fri, 1 Aug 2025 09:48:15 +0000 (+0200)
Subject: bpf: Check netfilter ctx accesses are aligned
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=9e6448f7b1efb27f8d508b067ecd33ed664a4246;p=thirdparty%2Fkernel%2Flinux.git

bpf: Check netfilter ctx accesses are aligned

Similarly to the previous patch fixing the flow_dissector ctx accesses,
nf_is_valid_access also doesn't check that ctx accesses are aligned.
Contrary to flow_dissector programs, netfilter programs don't have
context conversion. The unaligned ctx accesses are therefore allowed by
the verifier.

Fixes: fd9c663b9ad6 ("bpf: minimal support for programs hooked into netfilter framework")
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/853ae9ed5edaa5196e8472ff0f1bb1cc24059214.1754039605.git.paul.chaignon@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---

diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
index 3e4fb9ddcd36f..46e667a50d988 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -296,6 +296,9 @@ static bool nf_is_valid_access(int off, int size, enum bpf_access_type type,
 	if (off < 0 || off >= sizeof(struct bpf_nf_ctx))
 		return false;
 
+	if (off % size != 0)
+		return false;
+
 	if (type == BPF_WRITE)
 		return false;