Commit 17c3df70 authored Apr 14, 2021 by Paolo Abeni Committed by David S. Miller Apr 14, 2021

skbuff: revert "skbuff: remove some unnecessary operation in skb_segment_list()"



the commit 1ddc3229 ("skbuff: remove some unnecessary operation
in skb_segment_list()") introduces an issue very similar to the
one already fixed by commit 53475c5d ("net: fix use-after-free when
UDP GRO with shared fraglist").

If the GSO skb goes though skb_clone() and pskb_expand_head() before
entering skb_segment_list(), the latter  will unshare the frag_list
skbs and will release the old list. With the reverted commit in place,
when skb_segment_list() completes, skb->next points to the just
released list, and later on the kernel will hit UaF.

Note that since commit e0e3070a ("udp: properly complete L4 GRO
over UDP tunnel packet") the critical scenario can be reproduced also
receiving UDP over vxlan traffic with:

NIC (NETIF_F_GRO_FRAGLIST enabled) -> vxlan -> UDP sink

Attaching a packet socket to the NIC will cause skb_clone() and the
tunnel decapsulation will call pskb_expand_head().

Fixes: 1ddc3229 ("skbuff: remove some unnecessary operation in skb_segment_list()")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 73d7de66

net/core/skbuff.c

+12 −3

Original line number	Diff line number	Diff line
		@@ -3773,13 +3773,13 @@ struct sk_buff skb_segment_list(struct sk_buff skb,
		unsigned int tnl_hlen = skb_tnl_header_len(skb);
		unsigned int delta_truesize = 0;
		unsigned int delta_len = 0;
		struct sk_buff *tail = NULL;
		struct sk_buff nskb, tmp;
		int err;

		skb_push(skb, -skb_network_offset(skb) + offset);

		skb_shinfo(skb)->frag_list = NULL;
		skb->next = list_skb;

		do {
		nskb = list_skb;
		@@ -3797,8 +3797,17 @@ struct sk_buff skb_segment_list(struct sk_buff skb,
		}
		}

		if (unlikely(err))
		if (!tail)
		skb->next = nskb;
		else
		tail->next = nskb;

		if (unlikely(err)) {
		nskb->next = list_skb;
		goto err_linearize;
		}

		tail = nskb;

		delta_len += nskb->len;
		delta_truesize += nskb->truesize;
		@@ -3825,7 +3834,7 @@ struct sk_buff skb_segment_list(struct sk_buff skb,

		skb_gso_reset(skb);

		skb->prev = nskb;
		skb->prev = tail;

		if (skb_needs_linearize(skb, features) &&
		__skb_linearize(skb))