path: root/drivers/net/macsec.c
diff options
authorJason A. Donenfeld <Jason@zx2c4.com>2017-04-21 23:14:48 +0200
committerDavid S. Miller <davem@davemloft.net>2017-04-24 13:46:58 -0400
commit4d6fa57b4dab0d77f4d8e9d9c73d1e63f6fe8fee (patch)
treec5516c47d1680f2b0d4a959242a51035d4d2a744 /drivers/net/macsec.c
parentipv4: Avoid caching l3mdev dst on mismatched local route (diff)
macsec: avoid heap overflow in skb_to_sgvec
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>
Diffstat (limited to '')
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index ff0a5ed3ca80..dbab05afcdbe 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,
static struct lock_class_key macsec_netdev_addr_lock_key;
static int macsec_dev_init(struct net_device *dev)