Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1947892AbdDYOVZ (ORCPT ); Tue, 25 Apr 2017 10:21:25 -0400 Received: from frisell.zx2c4.com ([192.95.5.64]:50103 "EHLO frisell.zx2c4.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1947870AbdDYOVR (ORCPT ); Tue, 25 Apr 2017 10:21:17 -0400 From: "Jason A. Donenfeld" To: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net, David.Laight@aculab.com, kernel-hardening@lists.openwall.com Cc: "Jason A. Donenfeld" Subject: [PATCH v3 1/5] skbuff: return -EMSGSIZE in skb_to_sgvec to prevent overflow Date: Tue, 25 Apr 2017 16:21:12 +0200 Message-Id: <20170425142112.29702-1-Jason@zx2c4.com> X-Mailer: git-send-email 2.12.2 In-Reply-To: <20170425141609.28459-1-Jason@zx2c4.com> References: <20170425141609.28459-1-Jason@zx2c4.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2164 Lines: 62 This is a defense-in-depth measure in response to bugs like 4d6fa57b4dab0d77f4d8e9d9c73d1e63f6fe8fee. Signed-off-by: Jason A. Donenfeld --- 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