The gateway client code can try to optimize the delivery of DHCP packets to avoid broadcasting them through the whole mesh. But also transmissions to the client can be optimized by looking up the destination via the chaddr of the DHCP packet.

But the chaddr is currently only done when chaddr is fully inside the non-paged area of the skbuff. Otherwise it will not be initialized and the unoptimized path should have been taken.

But the implementation didn't handle this correctly. It didn't retrieve the correct chaddr but still tried to perform the TT lookup with this uninitialized memory.

Reported-by: syzbot+ab16e463b903f5a37036@syzkaller.appspotmail.com Fixes: 2d5b555644b2 ("batman-adv: send every DHCP packet as bat-unicast") Signed-off-by: Sven Eckelmann sven@narfation.org --- net/batman-adv/gateway_client.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c index a18dcc68..ef3f85b5 100644 --- a/net/batman-adv/gateway_client.c +++ b/net/batman-adv/gateway_client.c @@ -703,8 +703,10 @@ batadv_gw_dhcp_recipient_get(struct sk_buff *skb, unsigned int *header_len,

chaddr_offset = *header_len + BATADV_DHCP_CHADDR_OFFSET; /* store the client address if the message is going to a client */ - if (ret == BATADV_DHCP_TO_CLIENT && - pskb_may_pull(skb, chaddr_offset + ETH_ALEN)) { + if (ret == BATADV_DHCP_TO_CLIENT) { + if (!pskb_may_pull(skb, chaddr_offset + ETH_ALEN)) + return BATADV_DHCP_NO; + /* check if the DHCP packet carries an Ethernet DHCP */ p = skb->data + *header_len + BATADV_DHCP_HTYPE_OFFSET; if (*p != BATADV_DHCP_HTYPE_ETHERNET)