net/packet: Annotate struct packet_fanout with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct packet_fanout.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Anqi Shen <amy.saq@antgroup.com>
Cc: netdev@vger.kernel.org
Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/packet/internal.h b/net/packet/internal.h
index 63f4865..d29c94c 100644 (file)
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -94,7 +94,7 @@ struct packet_fanout {
        spinlock_t              lock;
        refcount_t              sk_ref;
        struct packet_type      prot_hook ____cacheline_aligned_in_smp;
-       struct sock     __rcu   *arr[];
+       struct sock     __rcu   *arr[] __counted_by(max_num_members);
 };
 
 struct packet_rollover {