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, 9 insertions, 7 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 7a93359fbc72..1771549d2438 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1188,22 +1188,25 @@ rarok:
         goto out;
 }
 
-static int inet_gifconf(struct net_device *dev, char __user *buf, int len)
+static int inet_gifconf(struct net_device *dev, char __user *buf, int len, int size)
 {
         struct in_device *in_dev = __in_dev_get_rtnl(dev);
         struct in_ifaddr *ifa;
         struct ifreq ifr;
         int done = 0;
 
+        if (WARN_ON(size > sizeof(struct ifreq)))
+                goto out;
+
         if (!in_dev)
                 goto out;
 
         for (ifa = in_dev->ifa_list; ifa; ifa = ifa->ifa_next) {
                 if (!buf) {
-                        done += sizeof(ifr);
+                        done += size;
                         continue;
                 }
-                if (len < (int) sizeof(ifr))
+                if (len < size)
                         break;
                 memset(&ifr, 0, sizeof(struct ifreq));
                 strcpy(ifr.ifr_name, ifa->ifa_label);
@@ -1212,13 +1215,12 @@ static int inet_gifconf(struct net_device *dev, char __user *buf, int len)
                 (*(struct sockaddr_in *)&ifr.ifr_addr).sin_addr.s_addr =
                                                                 ifa->ifa_local;
 
-                if (copy_to_user(buf, &ifr, sizeof(struct ifreq))) {
+                if (copy_to_user(buf + done, &ifr, size)) {
                         done = -EFAULT;
                         break;
                 }
-                buf  += sizeof(struct ifreq);
-                len  -= sizeof(struct ifreq);
-                done += sizeof(struct ifreq);
+                len  -= size;
+                done += size;
         }
 out:
         return done;