dev_ioctl: copy only the smaller struct iwreq for wext

Unfortunately, struct iwreq isn't a proper subset of struct ifreq,
but is still handled by the same code path. Robert reported that
then applications may (randomly) fault if the struct iwreq they
pass happens to land within 8 bytes of the end of a mapping (the
struct is only 32 bytes, vs. struct ifreq's 40 bytes).

To fix this, pull out the code handling wireless extension ioctls
and copy only the smaller structure in this case.

This bug goes back a long time, I tracked that it was introduced
into mainline in 2.1.15, over 20 years ago!

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=195869

Reported-by: Robert O'Callahan <robert@ocallahan.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 16 insertions, 3 deletions

diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index b94b1d293506..27fad31784a8 100644
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -410,6 +410,22 @@ int dev_ioctl(struct net *net, unsigned int cmd, void __user *arg)
 	if (cmd == SIOCGIFNAME)
 		return dev_ifname(net, (struct ifreq __user *)arg);
 
+	/*
+	 * Take care of Wireless Extensions. Unfortunately struct iwreq
+	 * isn't a proper subset of struct ifreq (it's 8 byte shorter)
+	 * so we need to treat it specially, otherwise applications may
+	 * fault if the struct they're passing happens to land at the
+	 * end of a mapped page.
+	 */
+	if (cmd >= SIOCIWFIRST && cmd <= SIOCIWLAST) {
+		struct iwreq iwr;
+
+		if (copy_from_user(&iwr, arg, sizeof(iwr)))
+			return -EFAULT;
+
+		return wext_handle_ioctl(net, &iwr, cmd, arg);
+	}
+
 	if (copy_from_user(&ifr, arg, sizeof(struct ifreq)))
 		return -EFAULT;
 
@@ -559,9 +575,6 @@ int dev_ioctl(struct net *net, unsigned int cmd, void __user *arg)
 				ret = -EFAULT;
 			return ret;
 		}
-		/* Take care of Wireless Extensions */
-		if (cmd >= SIOCIWFIRST && cmd <= SIOCIWLAST)
-			return wext_handle_ioctl(net, &ifr, cmd, arg);
 		return -ENOTTY;
 	}
 }