From 4d6fa57b4dab0d77f4d8e9d9c73d1e63f6fe8fee Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 21 Apr 2017 23:14:48 +0200 Subject: 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 Cc: stable@vger.kernel.org Cc: security@kernel.org Signed-off-by: David S. Miller --- drivers/net/macsec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/net/macsec.c') 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, } #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) -- cgit v1.2.3 From 5294b83086cc1c35b4efeca03644cf9d12282e5b Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 25 Apr 2017 19:08:18 +0200 Subject: macsec: dynamically allocate space for sglist We call skb_cow_data, which is good anyway to ensure we can actually modify the skb as such (another error from prior). Now that we have the number of fragments required, we can safely allocate exactly that amount of memory. Fixes: c09440f7dcb3 ("macsec: introduce IEEE 802.1AE driver") Signed-off-by: Jason A. Donenfeld Acked-by: Sabrina Dubroca Signed-off-by: David S. Miller --- drivers/net/macsec.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-) (limited to 'drivers/net/macsec.c') diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c index dbab05afcdbe..49ce4e9f4a0f 100644 --- a/drivers/net/macsec.c +++ b/drivers/net/macsec.c @@ -617,7 +617,8 @@ static void macsec_encrypt_done(struct crypto_async_request *base, int err) static struct aead_request *macsec_alloc_req(struct crypto_aead *tfm, unsigned char **iv, - struct scatterlist **sg) + struct scatterlist **sg, + int num_frags) { size_t size, iv_offset, sg_offset; struct aead_request *req; @@ -629,7 +630,7 @@ static struct aead_request *macsec_alloc_req(struct crypto_aead *tfm, size = ALIGN(size, __alignof__(struct scatterlist)); sg_offset = size; - size += sizeof(struct scatterlist) * (MAX_SKB_FRAGS + 1); + size += sizeof(struct scatterlist) * num_frags; tmp = kmalloc(size, GFP_ATOMIC); if (!tmp) @@ -649,6 +650,7 @@ static struct sk_buff *macsec_encrypt(struct sk_buff *skb, { int ret; struct scatterlist *sg; + struct sk_buff *trailer; unsigned char *iv; struct ethhdr *eth; struct macsec_eth_header *hh; @@ -723,7 +725,14 @@ static struct sk_buff *macsec_encrypt(struct sk_buff *skb, return ERR_PTR(-EINVAL); } - req = macsec_alloc_req(tx_sa->key.tfm, &iv, &sg); + ret = skb_cow_data(skb, 0, &trailer); + if (unlikely(ret < 0)) { + macsec_txsa_put(tx_sa); + kfree_skb(skb); + return ERR_PTR(ret); + } + + req = macsec_alloc_req(tx_sa->key.tfm, &iv, &sg, ret); if (!req) { macsec_txsa_put(tx_sa); kfree_skb(skb); @@ -732,7 +741,7 @@ static struct sk_buff *macsec_encrypt(struct sk_buff *skb, macsec_fill_iv(iv, secy->sci, pn); - sg_init_table(sg, MAX_SKB_FRAGS + 1); + sg_init_table(sg, ret); skb_to_sgvec(skb, sg, 0, skb->len); if (tx_sc->encrypt) { @@ -917,6 +926,7 @@ static struct sk_buff *macsec_decrypt(struct sk_buff *skb, { int ret; struct scatterlist *sg; + struct sk_buff *trailer; unsigned char *iv; struct aead_request *req; struct macsec_eth_header *hdr; @@ -927,7 +937,12 @@ static struct sk_buff *macsec_decrypt(struct sk_buff *skb, if (!skb) return ERR_PTR(-ENOMEM); - req = macsec_alloc_req(rx_sa->key.tfm, &iv, &sg); + ret = skb_cow_data(skb, 0, &trailer); + if (unlikely(ret < 0)) { + kfree_skb(skb); + return ERR_PTR(ret); + } + req = macsec_alloc_req(rx_sa->key.tfm, &iv, &sg, ret); if (!req) { kfree_skb(skb); return ERR_PTR(-ENOMEM); @@ -936,7 +951,7 @@ static struct sk_buff *macsec_decrypt(struct sk_buff *skb, hdr = (struct macsec_eth_header *)skb->data; macsec_fill_iv(iv, sci, ntohl(hdr->packet_number)); - sg_init_table(sg, MAX_SKB_FRAGS + 1); + sg_init_table(sg, ret); skb_to_sgvec(skb, sg, 0, skb->len); if (hdr->tci_an & MACSEC_TCI_E) { @@ -2716,7 +2731,7 @@ static netdev_tx_t macsec_start_xmit(struct sk_buff *skb, } #define MACSEC_FEATURES \ - (NETIF_F_SG | NETIF_F_HIGHDMA) + (NETIF_F_SG | NETIF_F_HIGHDMA | NETIF_F_FRAGLIST) static struct lock_class_key macsec_netdev_addr_lock_key; static int macsec_dev_init(struct net_device *dev) -- cgit v1.2.3