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Message-Id: <20170425142112.29702-1-Jason@zx2c4.com>
Date: Tue, 25 Apr 2017 16:21:12 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
davem@...emloft.net,
David.Laight@...lab.com,
kernel-hardening@...ts.openwall.com
Cc: "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH v3 1/5] skbuff: return -EMSGSIZE in skb_to_sgvec to prevent overflow
This is a defense-in-depth measure in response to bugs like
4d6fa57b4dab0d77f4d8e9d9c73d1e63f6fe8fee.
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
Sorry for the completely stupid amount of churn - v1,v2,v3 in the span of
two minutes. It's just that after noticing first that nsg needs to be checked,
I also noticed something a bit worse: that there was a bug (exploitable?) where
if skb_to_sgvec was called with empty values, there would be an out-of-bounds
write into sg[0 - 1]. So, this third (and hopefully final!) patch fixes that
bug while we're at it.
net/core/skbuff.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f86bf69cfb8d..d103134deddb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3489,7 +3489,9 @@ void __init skb_init(void)
* @len: Length of buffer space to be mapped
*
* Fill the specified scatter-gather list with mappings/pointers into a
- * region of the buffer space attached to a socket buffer.
+ * region of the buffer space attached to a socket buffer. Returns either
+ * the number of scatterlist items used, or -EMSGSIZE if the contents
+ * could not fit.
*/
static int
__skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
@@ -3512,6 +3514,9 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
int end;
+ if (elt && sg_is_last(&sg[elt - 1]))
+ return -EMSGSIZE;
+
WARN_ON(start > offset + len);
end = start + skb_frag_size(&skb_shinfo(skb)->frags[i]);
@@ -3535,6 +3540,9 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
WARN_ON(start > offset + len);
+ if (elt && sg_is_last(&sg[elt - 1]))
+ return -EMSGSIZE;
+
end = start + frag_iter->len;
if ((copy = end - offset) > 0) {
if (copy > len)
@@ -3581,6 +3589,9 @@ int skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int le
{
int nsg = __skb_to_sgvec(skb, sg, offset, len);
+ if (nsg <= 0)
+ return nsg;
+
sg_mark_end(&sg[nsg - 1]);
return nsg;
--
2.12.2
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