Patch "ipv6: fix out of bound writes in __ip6_append_data()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

ipv6: fix out of bound writes in __ip6_append_data()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     ipv6-fix-out-of-bound-writes-in-__ip6_append_data.patch

and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Fri, 19 May 2017 14:17:48 -0700
Subject: ipv6: fix out of bound writes in __ip6_append_data()

From: Eric Dumazet <[email protected]>

[ Upstream commit 232cd35d0804cc241eb887bb8d4d9b3b9881c64a ]

Andrey Konovalov and [email protected] 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.

---
 net/ipv6/ip6_output.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

@@ -1447,6 +1447,11 @@ alloc_new_skb:
 			 */
 			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,

@@ -1496,13 +1501,9 @@ alloc_new_skb:
 				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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/ipv6-fix-out-of-bound-writes-in-__ip6_append_data.patch queue-4.9/tcp-eliminate-negative-reordering-in-tcp_clean_rtx_queue.patch queue-4.9/dccp-tcp-do-not-inherit-mc_list-from-parent.patch queue-4.9/tcp-avoid-fragmenting-peculiar-skbs-in-sack.patch queue-4.9/netem-fix-skb_orphan_partial.patch queue-4.9/net-fix-compile-error-in-skb_orphan_partial.patch queue-4.9/ipv6-dccp-do-not-inherit-ipv6_mc_list-from-parent.patch queue-4.9/sctp-do-not-inherit-ipv6_-mc-ac-fl-_list-from-parent.patch queue-4.9/ipv4-add-reference-counting-to-metrics.patch queue-4.9/tcp-avoid-fastopen-api-to-be-used-on-af_unspec.patch