From 2bb2c56a2089211713a7b1fb379cce741f65ea9e Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 19 May 2017 14:17:48 -0700 Subject: [PATCH] ipv6: fix out of bound writes in __ip6_append_data() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Andrey Konovalov and idaifish@gmail.com reported crashes caused by one skb shared_info being overwritten from __ip6_append_data() Andrey program lead to following state : copy -4200 datalen 2000 fraglen 2040 maxfraglen 2040 alloclen 2048 transhdrlen 0 offset 0 fraggap 6200 The skb_copy_and_csum_bits(skb_prev, maxfraglen, data + transhdrlen, fraggap, 0); is overwriting skb->head and skb_shared_info Since we apparently detect this rare condition too late, move the code earlier to even avoid allocating skb and risking crashes. Once again, many thanks to Andrey and syzkaller team. Signed-off-by: Eric Dumazet Reported-by: Andrey Konovalov Tested-by: Andrey Konovalov Reported-by: Signed-off-by: David S. Miller CVE-2017-9242 (cherry-picked from 232cd35d0804cc241eb887bb8d4d9b3b9881c64a) Signed-off-by: Stefan Bader Acked-by: Colin King Acked-by: Andy Whitcroft Signed-off-by: Thadeu Lima de Souza Cascardo Signed-off-by: Fabian Grünbichler --- net/ipv6/ip6_output.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index 8f0814d301aa..135ee573eaef 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -1463,6 +1463,11 @@ static int __ip6_append_data(struct sock *sk, */ alloclen += sizeof(struct frag_hdr); + copy = datalen - transhdrlen - fraggap; + if (copy < 0) { + err = -EINVAL; + goto error; + } if (transhdrlen) { skb = sock_alloc_send_skb(sk, alloclen + hh_len, @@ -1512,13 +1517,9 @@ static int __ip6_append_data(struct sock *sk, data += fraggap; pskb_trim_unique(skb_prev, maxfraglen); } - copy = datalen - transhdrlen - fraggap; - - if (copy < 0) { - err = -EINVAL; - kfree_skb(skb); - goto error; - } else if (copy > 0 && getfrag(from, data + transhdrlen, offset, copy, fraggap, skb) < 0) { + if (copy > 0 && + getfrag(from, data + transhdrlen, offset, + copy, fraggap, skb) < 0) { err = -EFAULT; kfree_skb(skb); goto error; -- 2.11.0