74 lines
3.0 KiB
Diff
74 lines
3.0 KiB
Diff
|
From 4d6fa57b4dab0d77f4d8e9d9c73d1e63f6fe8fee Mon Sep 17 00:00:00 2001
|
||
|
|
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
|
||
|
|
|
||
|
|
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)
|
||
|
|
--
|
||
|
|
cgit v1.1
|
||
|
|
|