74 lines
3.0 KiB
Diff
74 lines
3.0 KiB
Diff
From 4d6fa57b4dab0d77f4d8e9d9c73d1e63f6fe8fee Mon Sep 17 00:00:00 2001
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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
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Date: Fri, 21 Apr 2017 23:14:48 +0200
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Subject: macsec: avoid heap overflow in skb_to_sgvec
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While this may appear as a humdrum one line change, it's actually quite
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important. An sk_buff stores data in three places:
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1. A linear chunk of allocated memory in skb->data. This is the easiest
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one to work with, but it precludes using scatterdata since the memory
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must be linear.
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2. The array skb_shinfo(skb)->frags, which is of maximum length
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MAX_SKB_FRAGS. This is nice for scattergather, since these fragments
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can point to different pages.
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3. skb_shinfo(skb)->frag_list, which is a pointer to another sk_buff,
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which in turn can have data in either (1) or (2).
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The first two are rather easy to deal with, since they're of a fixed
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maximum length, while the third one is not, since there can be
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potentially limitless chains of fragments. Fortunately dealing with
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frag_list is opt-in for drivers, so drivers don't actually have to deal
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with this mess. For whatever reason, macsec decided it wanted pain, and
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so it explicitly specified NETIF_F_FRAGLIST.
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Because dealing with (1), (2), and (3) is insane, most users of sk_buff
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doing any sort of crypto or paging operation calls a convenient function
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called skb_to_sgvec (which happens to be recursive if (3) is in use!).
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This takes a sk_buff as input, and writes into its output pointer an
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array of scattergather list items. Sometimes people like to declare a
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fixed size scattergather list on the stack; othertimes people like to
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allocate a fixed size scattergather list on the heap. However, if you're
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doing it in a fixed-size fashion, you really shouldn't be using
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NETIF_F_FRAGLIST too (unless you're also ensuring the sk_buff and its
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frag_list children arent't shared and then you check the number of
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fragments in total required.)
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Macsec specifically does this:
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size += sizeof(struct scatterlist) * (MAX_SKB_FRAGS + 1);
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tmp = kmalloc(size, GFP_ATOMIC);
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*sg = (struct scatterlist *)(tmp + sg_offset);
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...
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sg_init_table(sg, MAX_SKB_FRAGS + 1);
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skb_to_sgvec(skb, sg, 0, skb->len);
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Specifying MAX_SKB_FRAGS + 1 is the right answer usually, but not if you're
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using NETIF_F_FRAGLIST, in which case the call to skb_to_sgvec will
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overflow the heap, and disaster ensues.
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Cc: stable@vger.kernel.org
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Cc: security@kernel.org
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Signed-off-by: David S. Miller <davem@davemloft.net>
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---
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drivers/net/macsec.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
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index ff0a5ed..dbab05a 100644
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--- a/drivers/net/macsec.c
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+++ b/drivers/net/macsec.c
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@@ -2716,7 +2716,7 @@ static netdev_tx_t macsec_start_xmit(struct sk_buff *skb,
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}
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#define MACSEC_FEATURES \
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- (NETIF_F_SG | NETIF_F_HIGHDMA | NETIF_F_FRAGLIST)
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+ (NETIF_F_SG | NETIF_F_HIGHDMA)
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static struct lock_class_key macsec_netdev_addr_lock_key;
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static int macsec_dev_init(struct net_device *dev)
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--
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cgit v1.1
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