linux-kernel - [PATCH v3 1/5] skbuff: return -EMSGSIZE in skb_to

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

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