net/ipv6/mcast: Use struct_size() helper

Replace IP6_SFLSIZE() with struct_size() helper in order to avoid any
potential type mistakes or integer overflows that, in the worst
scenario, could lead to heap overflows.
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/if_inet6.h

@@ -82,9 +82,6 @@ struct ip6_sf_socklist {
 	struct in6_addr		sl_addr[];
 };
 
-#define IP6_SFLSIZE(count)	(sizeof(struct ip6_sf_socklist) + \
-	(count) * sizeof(struct in6_addr))
-
 #define IP6_SFBLOCK	10	/* allocate this many at once */
 
 struct ipv6_mc_socklist {

net/ipv6/mcast.c

@@ -447,7 +447,8 @@ int ip6_mc_source(int add, int omode, struct sock *sk,
 
 		if (psl)
 			count += psl->sl_max;
-		newpsl = sock_kmalloc(sk, IP6_SFLSIZE(count), GFP_KERNEL);
+		newpsl = sock_kmalloc(sk, struct_size(newpsl, sl_addr, count),
+				      GFP_KERNEL);
 		if (!newpsl) {
 			err = -ENOBUFS;
 			goto done;
@@ -457,7 +458,8 @@ int ip6_mc_source(int add, int omode, struct sock *sk,
 		if (psl) {
 			for (i = 0; i < psl->sl_count; i++)
 				newpsl->sl_addr[i] = psl->sl_addr[i];
-			atomic_sub(IP6_SFLSIZE(psl->sl_max), &sk->sk_omem_alloc);
+			atomic_sub(struct_size(psl, sl_addr, psl->sl_max),
+				   &sk->sk_omem_alloc);
 			kfree_rcu(psl, rcu);
 		}
 		psl = newpsl;
@@ -525,7 +527,8 @@ int ip6_mc_msfilter(struct sock *sk, struct group_filter *gsf,
 		goto done;
 	}
 	if (gsf->gf_numsrc) {
-		newpsl = sock_kmalloc(sk, IP6_SFLSIZE(gsf->gf_numsrc),
+		newpsl = sock_kmalloc(sk, struct_size(newpsl, sl_addr,
+						      gsf->gf_numsrc),
 				      GFP_KERNEL);
 		if (!newpsl) {
 			err = -ENOBUFS;
@@ -543,7 +546,8 @@ int ip6_mc_msfilter(struct sock *sk, struct group_filter *gsf,
 				     newpsl->sl_count, newpsl->sl_addr, 0);
 		if (err) {
 			mutex_unlock(&idev->mc_lock);
-			sock_kfree_s(sk, newpsl, IP6_SFLSIZE(newpsl->sl_max));
+			sock_kfree_s(sk, newpsl, struct_size(newpsl, sl_addr,
+							     newpsl->sl_max));
 			goto done;
 		}
 		mutex_unlock(&idev->mc_lock);
@@ -559,7 +563,8 @@ int ip6_mc_msfilter(struct sock *sk, struct group_filter *gsf,
 	if (psl) {
 		ip6_mc_del_src(idev, group, pmc->sfmode,
 			       psl->sl_count, psl->sl_addr, 0);
-		atomic_sub(IP6_SFLSIZE(psl->sl_max), &sk->sk_omem_alloc);
+		atomic_sub(struct_size(psl, sl_addr, psl->sl_max),
+			   &sk->sk_omem_alloc);
 		kfree_rcu(psl, rcu);
 	} else {
 		ip6_mc_del_src(idev, group, pmc->sfmode, 0, NULL, 0);
@@ -2607,7 +2612,8 @@ static int ip6_mc_leave_src(struct sock *sk, struct ipv6_mc_socklist *iml,
 		err = ip6_mc_del_src(idev, &iml->addr, iml->sfmode,
 				     psl->sl_count, psl->sl_addr, 0);
 		RCU_INIT_POINTER(iml->sflist, NULL);
-		atomic_sub(IP6_SFLSIZE(psl->sl_max), &sk->sk_omem_alloc);
+		atomic_sub(struct_size(psl, sl_addr, psl->sl_max),
+			   &sk->sk_omem_alloc);
 		kfree_rcu(psl, rcu);
 	}