net/ipv4/igmp: Use struct_size() helper

Replace IP_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/linux/igmp.h

@@ -41,9 +41,6 @@ struct ip_sf_socklist {
 	__be32			sl_addr[];
 };
 
-#define IP_SFLSIZE(count)	(sizeof(struct ip_sf_socklist) + \
-	(count) * sizeof(__be32))
-
 #define IP_SFBLOCK	10	/* allocate this many at once */
 
 /* ip_mc_socklist is real list now. Speed is not argument;

net/ipv4/igmp.c

@@ -2233,7 +2233,7 @@ static int ip_mc_leave_src(struct sock *sk, struct ip_mc_socklist *iml,
 			iml->sfmode, psf->sl_count, psf->sl_addr, 0);
 	RCU_INIT_POINTER(iml->sflist, NULL);
 	/* decrease mem now to avoid the memleak warning */
-	atomic_sub(IP_SFLSIZE(psf->sl_max), &sk->sk_omem_alloc);
+	atomic_sub(struct_size(psf, sl_addr, psf->sl_max), &sk->sk_omem_alloc);
 	kfree_rcu(psf, rcu);
 	return err;
 }
@@ -2382,7 +2382,8 @@ int ip_mc_source(int add, int omode, struct sock *sk, struct
 
 		if (psl)
 			count += psl->sl_max;
-		newpsl = sock_kmalloc(sk, IP_SFLSIZE(count), GFP_KERNEL);
+		newpsl = sock_kmalloc(sk, struct_size(newpsl, sl_addr, count),
+				      GFP_KERNEL);
 		if (!newpsl) {
 			err = -ENOBUFS;
 			goto done;
@@ -2393,7 +2394,8 @@ int ip_mc_source(int add, int omode, struct sock *sk, struct
 			for (i = 0; i < psl->sl_count; i++)
 				newpsl->sl_addr[i] = psl->sl_addr[i];
 			/* decrease mem now to avoid the memleak warning */
-			atomic_sub(IP_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);
 		}
 		rcu_assign_pointer(pmc->sflist, newpsl);
@@ -2468,8 +2470,9 @@ int ip_mc_msfilter(struct sock *sk, struct ip_msfilter *msf, int ifindex)
 		goto done;
 	}
 	if (msf->imsf_numsrc) {
-		newpsl = sock_kmalloc(sk, IP_SFLSIZE(msf->imsf_numsrc),
-							   GFP_KERNEL);
+		newpsl = sock_kmalloc(sk, struct_size(newpsl, sl_addr,
+						      msf->imsf_numsrc),
+				      GFP_KERNEL);
 		if (!newpsl) {
 			err = -ENOBUFS;
 			goto done;
@@ -2480,7 +2483,9 @@ int ip_mc_msfilter(struct sock *sk, struct ip_msfilter *msf, int ifindex)
 		err = ip_mc_add_src(in_dev, &msf->imsf_multiaddr,
 			msf->imsf_fmode, newpsl->sl_count, newpsl->sl_addr, 0);
 		if (err) {
-			sock_kfree_s(sk, newpsl, IP_SFLSIZE(newpsl->sl_max));
+			sock_kfree_s(sk, newpsl,
+				     struct_size(newpsl, sl_addr,
+						 newpsl->sl_max));
 			goto done;
 		}
 	} else {
@@ -2493,7 +2498,8 @@ int ip_mc_msfilter(struct sock *sk, struct ip_msfilter *msf, int ifindex)
 		(void) ip_mc_del_src(in_dev, &msf->imsf_multiaddr, pmc->sfmode,
 			psl->sl_count, psl->sl_addr, 0);
 		/* decrease mem now to avoid the memleak warning */
-		atomic_sub(IP_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
 		(void) ip_mc_del_src(in_dev, &msf->imsf_multiaddr, pmc->sfmode,