macsec: avoid heap overflow in skb_to_sgvec (CVE-2017-7477)

debian/changelog

@@ -346,6 +346,7 @@ linux (4.9.24-1) UNRELEASED; urgency=medium
 
   [ Salvatore Bonaccorso ]
   * ping: implement proper locking (CVE-2017-2671)
+  * macsec: avoid heap overflow in skb_to_sgvec (CVE-2017-7477)
 
   [ Aurelien Jarno ]
   * [mips*/octeon] Drop obsolete patch adding support for the UBNT E200

debian/patches/bugfix/all/macsec-avoid-heap-overflow-in-skb_to_sgvec.patch

@@ -0,0 +1,74 @@
+From: "Jason A. Donenfeld" <Jason@zx2c4.com>
+Date: Fri, 21 Apr 2017 23:14:48 +0200
+Subject: macsec: avoid heap overflow in skb_to_sgvec
+Origin: https://git.kernel.org/linus/4d6fa57b4dab0d77f4d8e9d9c73d1e63f6fe8fee
+Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2017-7477
+
+While this may appear as a humdrum one line change, it's actually quite
+important. An sk_buff stores data in three places:
+
+1. A linear chunk of allocated memory in skb->data. This is the easiest
+   one to work with, but it precludes using scatterdata since the memory
+   must be linear.
+2. The array skb_shinfo(skb)->frags, which is of maximum length
+   MAX_SKB_FRAGS. This is nice for scattergather, since these fragments
+   can point to different pages.
+3. skb_shinfo(skb)->frag_list, which is a pointer to another sk_buff,
+   which in turn can have data in either (1) or (2).
+
+The first two are rather easy to deal with, since they're of a fixed
+maximum length, while the third one is not, since there can be
+potentially limitless chains of fragments. Fortunately dealing with
+frag_list is opt-in for drivers, so drivers don't actually have to deal
+with this mess. For whatever reason, macsec decided it wanted pain, and
+so it explicitly specified NETIF_F_FRAGLIST.
+
+Because dealing with (1), (2), and (3) is insane, most users of sk_buff
+doing any sort of crypto or paging operation calls a convenient function
+called skb_to_sgvec (which happens to be recursive if (3) is in use!).
+This takes a sk_buff as input, and writes into its output pointer an
+array of scattergather list items. Sometimes people like to declare a
+fixed size scattergather list on the stack; othertimes people like to
+allocate a fixed size scattergather list on the heap. However, if you're
+doing it in a fixed-size fashion, you really shouldn't be using
+NETIF_F_FRAGLIST too (unless you're also ensuring the sk_buff and its
+frag_list children arent't shared and then you check the number of
+fragments in total required.)
+
+Macsec specifically does this:
+
+        size += sizeof(struct scatterlist) * (MAX_SKB_FRAGS + 1);
+        tmp = kmalloc(size, GFP_ATOMIC);
+        *sg = (struct scatterlist *)(tmp + sg_offset);
+	...
+        sg_init_table(sg, MAX_SKB_FRAGS + 1);
+        skb_to_sgvec(skb, sg, 0, skb->len);
+
+Specifying MAX_SKB_FRAGS + 1 is the right answer usually, but not if you're
+using NETIF_F_FRAGLIST, in which case the call to skb_to_sgvec will
+overflow the heap, and disaster ensues.
+
+Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
+Cc: stable@vger.kernel.org
+Cc: security@kernel.org
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/macsec.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
+index ff0a5ed..dbab05a 100644
+--- a/drivers/net/macsec.c
++++ b/drivers/net/macsec.c
+@@ -2716,7 +2716,7 @@ static netdev_tx_t macsec_start_xmit(struct sk_buff *skb,
+ }
+ 
+ #define MACSEC_FEATURES \
+-	(NETIF_F_SG | NETIF_F_HIGHDMA | NETIF_F_FRAGLIST)
++	(NETIF_F_SG | NETIF_F_HIGHDMA)
+ static struct lock_class_key macsec_netdev_addr_lock_key;
+ 
+ static int macsec_dev_init(struct net_device *dev)
+-- 
+2.1.4
+

debian/patches/series

@@ -110,6 +110,7 @@ bugfix/all/net-packet-fix-overflow-in-check-for-tp_reserve.patch
 bugfix/all/ping-implement-proper-locking.patch
 bugfix/all/keys-disallow-keyrings-beginning-with-.-to-be-joined.patch
 bugfix/all/keys-fix-keyctl_set_reqkey_keyring-to-not-leak-threa.patch
+bugfix/all/macsec-avoid-heap-overflow-in-skb_to_sgvec.patch
 
 # Fix exported symbol versions
 bugfix/ia64/revert-ia64-move-exports-to-definitions.patch