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" <[email protected]>

Cc Eric Dumazet <[email protected]>

Cc Jakub Kicinski <[email protected]>

Cc Paolo Abeni <[email protected]>

Cc Johannes Berg <[email protected]>

Cc [email protected]

Link https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]

Signed-off-by Kees Cook <[email protected]>

---
  net/netlink/policy.c | 15 ++++++++-------
  1 file changed, 8 insertions(+), 7 deletions(-)

net/netlink/policy.c +8 -7

index 87e3de0fde89..e2f111edf66c 100644
@@ -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;