do_ip_setsockopt(): don't open-code memdup_user()

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

net/ipv4/ip_sockglue.c

@@ -934,14 +934,9 @@ static int do_ip_setsockopt(struct sock *sk, int level,
 			err = -ENOBUFS;
 			break;
 		}
-		msf = kmalloc(optlen, GFP_KERNEL);
-		if (!msf) {
-			err = -ENOBUFS;
-			break;
-		}
-		err = -EFAULT;
-		if (copy_from_user(msf, optval, optlen)) {
-			kfree(msf);
+		msf = memdup_user(optval, optlen);
+		if (IS_ERR(msf)) {
+			err = PTR_ERR(msf);
 			break;
 		}
 		/* numsrc >= (1G-4) overflow in 32 bits */
@@ -1090,14 +1085,11 @@ static int do_ip_setsockopt(struct sock *sk, int level,
 			err = -ENOBUFS;
 			break;
 		}
-		gsf = kmalloc(optlen, GFP_KERNEL);
-		if (!gsf) {
-			err = -ENOBUFS;
+		gsf = memdup_user(optval, optlen);
+		if (IS_ERR(gsf)) {
+			err = PTR_ERR(gsf);
 			break;
 		}
-		err = -EFAULT;
-		if (copy_from_user(gsf, optval, optlen))
-			goto mc_msf_out;
 
 		/* numsrc >= (4G-140)/128 overflow in 32 bits */
 		if (gsf->gf_numsrc >= 0x1ffffff ||