Commit 3915341a authored Apr 16, 2022 by Sven Eckelmann Committed by Greg Kroah-Hartman May 18, 2022

batman-adv: Don't skb_split skbuffs with frag_list



[ Upstream commit a063f2fba3fa633a599253b62561051ac185fa99 ]

The receiving interface might have used GRO to receive more fragments than
MAX_SKB_FRAGS fragments. In this case, these will not be stored in
skb_shinfo(skb)->frags but merged into the frag list.

batman-adv relies on the function skb_split to split packets up into
multiple smaller packets which are not larger than the MTU on the outgoing
interface. But this function cannot handle frag_list entries and is only
operating on skb_shinfo(skb)->frags. If it is still trying to split such an
skb and xmit'ing it on an interface without support for NETIF_F_FRAGLIST,
then validate_xmit_skb() will try to linearize it. But this fails due to
inconsistent information. And __pskb_pull_tail will trigger a BUG_ON after
skb_copy_bits() returns an error.

In case of entries in frag_list, just linearize the skb before operating on
it with skb_split().

Reported-by: Felix Kaechele <felix@kaechele.ca>
Fixes: c6c8fea2 ("net: Add batman-adv meshing protocol")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Tested-by: Felix Kaechele <felix@kaechele.ca>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 90659487

net/batman-adv/fragmentation.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -478,6 +478,17 @@ int batadv_frag_send_packet(struct sk_buff *skb,
		goto free_skb;
		}

		/* GRO might have added fragments to the fragment list instead of
		* frags[]. But this is not handled by skb_split and must be
		* linearized to avoid incorrect length information after all
		* batman-adv fragments were created and submitted to the
		* hard-interface
		*/
		if (skb_has_frag_list(skb) && __skb_linearize(skb)) {
		ret = -ENOMEM;
		goto free_skb;
		}

		/* Create one header to be copied to all fragments */
		frag_header.packet_type = BATADV_UNICAST_FRAG;
		frag_header.version = BATADV_COMPAT_VERSION;