net: separate SIOCGIFCONF handling from dev_ioctl()

Only two of dev_ioctl() callers may pass SIOCGIFCONF to it.
Separating that codepath from the rest of dev_ioctl() allows both
to simplify dev_ioctl() itself (all other cases work with struct ifreq *)
*and* seriously simplify the compat side of that beast: all it takes
is passing to inet_gifconf() an extra argument - the size of individual
records (sizeof(struct ifreq) or sizeof(struct compat_ifreq)).  With
dev_ifconf() called directly from sock_do_ioctl()/compat_dev_ifconf()
that's easy to arrange.

As the result, compat side of SIOCGIFCONF doesn't need any
allocations, copy_in_user() back and forth, etc.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 23 insertions, 56 deletions

diff --git a/net/socket.c b/net/socket.c
index 1536515b64378..96e5b23a2a2e5 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -961,10 +961,22 @@ static long sock_do_ioctl(struct net *net, struct socket *sock,
 	 * If this ioctl is unknown try to hand it down
 	 * to the NIC driver.
 	 */
-	if (err == -ENOIOCTLCMD)
-		err = dev_ioctl(net, cmd, argp);
+	if (err != -ENOIOCTLCMD)
+		return err;
 
-	return err;
+	if (cmd == SIOCGIFCONF) {
+		struct ifconf ifc;
+		if (copy_from_user(&ifc, argp, sizeof(struct ifconf)))
+			return -EFAULT;
+		rtnl_lock();
+		err = dev_ifconf(net, &ifc, sizeof(struct ifreq));
+		rtnl_unlock();
+		if (!err && copy_to_user(argp, &ifc, sizeof(struct ifconf)))
+			err = -EFAULT;
+		return err;
+	}
+
+	return dev_ioctl(net, cmd, argp);
 }
 
 /*
@@ -2673,70 +2685,25 @@ static int dev_ifname32(struct net *net, struct compat_ifreq __user *uifr32)
 	return 0;
 }
 
-static int dev_ifconf(struct net *net, struct compat_ifconf __user *uifc32)
+static int compat_dev_ifconf(struct net *net, struct compat_ifconf __user *uifc32)
 {
 	struct compat_ifconf ifc32;
 	struct ifconf ifc;
-	struct ifconf __user *uifc;
-	struct compat_ifreq __user *ifr32;
-	struct ifreq __user *ifr;
-	unsigned int i, j;
 	int err;
 
 	if (copy_from_user(&ifc32, uifc32, sizeof(struct compat_ifconf)))
 		return -EFAULT;
 
-	memset(&ifc, 0, sizeof(ifc));
-	if (ifc32.ifcbuf == 0) {
-		ifc32.ifc_len = 0;
-		ifc.ifc_len = 0;
-		ifc.ifc_req = NULL;
-		uifc = compat_alloc_user_space(sizeof(struct ifconf));
-	} else {
-		size_t len = ((ifc32.ifc_len / sizeof(struct compat_ifreq)) + 1) *
-			sizeof(struct ifreq);
-		uifc = compat_alloc_user_space(sizeof(struct ifconf) + len);
-		ifc.ifc_len = len;
-		ifr = ifc.ifc_req = (void __user *)(uifc + 1);
-		ifr32 = compat_ptr(ifc32.ifcbuf);
-		for (i = 0; i < ifc32.ifc_len; i += sizeof(struct compat_ifreq)) {
-			if (copy_in_user(ifr, ifr32, sizeof(struct compat_ifreq)))
-				return -EFAULT;
-			ifr++;
-			ifr32++;
-		}
-	}
-	if (copy_to_user(uifc, &ifc, sizeof(struct ifconf)))
-		return -EFAULT;
+	ifc.ifc_len = ifc32.ifc_len;
+	ifc.ifc_req = compat_ptr(ifc32.ifcbuf);
 
-	err = dev_ioctl(net, SIOCGIFCONF, uifc);
+	rtnl_lock();
+	err = dev_ifconf(net, &ifc, sizeof(struct compat_ifreq));
+	rtnl_unlock();
 	if (err)
 		return err;
 
-	if (copy_from_user(&ifc, uifc, sizeof(struct ifconf)))
-		return -EFAULT;
-
-	ifr = ifc.ifc_req;
-	ifr32 = compat_ptr(ifc32.ifcbuf);
-	for (i = 0, j = 0;
-	     i + sizeof(struct compat_ifreq) <= ifc32.ifc_len && j < ifc.ifc_len;
-	     i += sizeof(struct compat_ifreq), j += sizeof(struct ifreq)) {
-		if (copy_in_user(ifr32, ifr, sizeof(struct compat_ifreq)))
-			return -EFAULT;
-		ifr32++;
-		ifr++;
-	}
-
-	if (ifc32.ifcbuf == 0) {
-		/* Translate from 64-bit structure multiple to
-		 * a 32-bit one.
-		 */
-		i = ifc.ifc_len;
-		i = ((i / sizeof(struct ifreq)) * sizeof(struct compat_ifreq));
-		ifc32.ifc_len = i;
-	} else {
-		ifc32.ifc_len = i;
-	}
+	ifc32.ifc_len = ifc.ifc_len;
 	if (copy_to_user(uifc32, &ifc32, sizeof(struct compat_ifconf)))
 		return -EFAULT;
 
@@ -3133,7 +3100,7 @@ static int compat_sock_ioctl_trans(struct file *file, struct socket *sock,
 	case SIOCGIFNAME:
 		return dev_ifname32(net, argp);
 	case SIOCGIFCONF:
-		return dev_ifconf(net, argp);
+		return compat_dev_ifconf(net, argp);
 	case SIOCETHTOOL:
 		return ethtool_ioctl(net, argp);
 	case SIOCWANDEV: