Patch "net: validate variable length ll headers" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

net: validate variable length ll headers

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-validate-variable-length-ll-headers.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Willem de Bruijn <[email protected]>
Date: Wed, 9 Mar 2016 21:58:32 -0500
Subject: net: validate variable length ll headers

From: Willem de Bruijn <[email protected]>

[ Upstream commit 2793a23aacbd754dbbb5cb75093deb7e4103bace ]

Netdevice parameter hard_header_len is variously interpreted both as an upper and lower bound on link layer header length. The field is used as upper bound when reserving room at allocation, as lower bound when validating user input in PF_PACKET.

Clarify the definition to be maximum header length. For validation of untrusted headers, add an optional validate member to header_ops.

Allow bypassing of validation by passing CAP_SYS_RAWIO, for instance for deliberate testing of corrupt input. In this case, pad trailing bytes, as some device drivers expect completely initialized headers.

See also http://comments.gmane.org/gmane.linux.network/401064

---
 include/linux/netdevice.h |   22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

@@ -265,6 +265,7 @@ struct header_ops {
 	void	(*cache_update)(struct hh_cache *hh,
 				const struct net_device *dev,
 				const unsigned char *haddr);
+	bool	(*validate)(const char *ll_header, unsigned int len);
 };
 
 /* These flag bits are private to the generic network queueing

@@ -1398,8 +1399,7 @@ enum netdev_priv_flags {
  *	@dma:		DMA channel
  *	@mtu:		Interface MTU value
  *	@type:		Interface hardware type
- *	@hard_header_len: Hardware header length, which means that this is the
- *			  minimum size of a packet.
+ *	@hard_header_len: Maximum hardware header length.
  *
  *	@needed_headroom: Extra headroom the hardware may need, but not in all
  *			  cases can this be guaranteed

@@ -2493,6 +2493,24 @@ static inline int dev_parse_header(const
 	return dev->header_ops->parse(skb, haddr);
 }
 
+/* ll_header must have at least hard_header_len allocated */
+static inline bool dev_validate_header(const struct net_device *dev,
+				       char *ll_header, int len)
+{
+	if (likely(len >= dev->hard_header_len))
+		return true;
+
+	if (capable(CAP_SYS_RAWIO)) {
+		memset(ll_header + len, 0, dev->hard_header_len - len);
+		return true;
+	}
+
+	if (dev->header_ops && dev->header_ops->validate)
+		return dev->header_ops->validate(ll_header, len);
+
+	return false;
+}
+
 typedef int gifconf_func_t(struct net_device * dev, char __user * bufptr, int len);
 int register_gifconf(unsigned int family, gifconf_func_t *gifconf);
 static inline int unregister_gifconf(unsigned int family)

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/ax25-add-link-layer-header-validation-function.patch queue-4.4/net-validate-variable-length-ll-headers.patch queue-4.4/packet-validate-variable-length-ll-headers.patch queue-4.4/macvtap-always-pass-ethernet-header-in-linear.patch queue-4.4/ipv6-udp-fix-udp_mib_ignoredmulti-updates.patch