netlink: Annotate struct netlink_policy_dump_state 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 netlink_policy_dump_state.

Additionally update the size of the usage array length before accessing
it. This requires remembering the old size for the memset() and later
assignments.

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: Johannes Berg <johannes.berg@intel.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/netlink/policy.c b/net/netlink/policy.c
index 87e3de0fde8963ec8ba967fe9c6610770b9e6475..e2f111edf66c5cd45fe0309843d74715c640a677 100644 (file)
--- a/net/netlink/policy.c
+++ b/net/netlink/policy.c
@@ -21,7 +21,7 @@ struct netlink_policy_dump_state {
        struct {
                const struct nla_policy *policy;
                unsigned int maxtype;
-       } policies[];
+       } policies[] __counted_by(n_alloc);
 };
 
 static int add_policy(struct netlink_policy_dump_state **statep,
@@ -29,7 +29,7 @@ static int add_policy(struct netlink_policy_dump_state **statep,
                      unsigned int maxtype)
 {
        struct netlink_policy_dump_state *state = *statep;
-       unsigned int n_alloc, i;
+       unsigned int old_n_alloc, n_alloc, i;
 
        if (!policy || !maxtype)
                return 0;
@@ -52,12 +52,13 @@ static int add_policy(struct netlink_policy_dump_state **statep,
        if (!state)
                return -ENOMEM;
 
-       memset(&state->policies[state->n_alloc], 0,
-              flex_array_size(state, policies, n_alloc - state->n_alloc));
-
-       state->policies[state->n_alloc].policy = policy;
-       state->policies[state->n_alloc].maxtype = maxtype;
+       old_n_alloc = state->n_alloc;
        state->n_alloc = n_alloc;
+       memset(&state->policies[old_n_alloc], 0,
+              flex_array_size(state, policies, n_alloc - old_n_alloc));
+
+       state->policies[old_n_alloc].policy = policy;
+       state->policies[old_n_alloc].maxtype = maxtype;
        *statep = state;
 
        return 0;