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 3e4fb9ddcd36f64d5cab3aac238d79c2f8d43f04..46e667a50d988e788e9dc87fbcd9ecab025a1d64 100644 (file)
--- 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;