Commit 232cd35d authored May 19, 2017 by Eric Dumazet Committed by David S. Miller May 22, 2017

ipv6: fix out of bound writes in __ip6_append_data()



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 <edumazet@google.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Reported-by:  <idaifish@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 6d18c732

net/ipv6/ip6_output.c

+8 −7

Original line number	Diff line number	Diff line
		@@ -1466,6 +1466,11 @@ 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,
		@@ -1515,13 +1520,9 @@ 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;

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