batadv_send_skb_prepare_unicast(_4addr) might reallocate the skb's data. If it does then our ethhdr pointer is not valid anymore in batadv_send_skb_unicast(), resulting in a kernel paging error.

Fixing this by refetching the ethhdr pointer after the potential reallocation.

Introduced by 3275e7cc84fb0574e9662e8e74c3b1dab38f7143 ("batman-adv: improve unicast packet (re)routing")

Reported-by: Linus Lüssing linus.luessing@web.de Signed-off-by: Antonio Quartulli antonio@meshcoding.com ---

***This patch is not supposed to be merged in the batman-adv repository***

This is a substitutive patch that I am going to send to net instead of the one that we have in maint (same subject). I am doing this because the original patch together with all the bugfixes that followed it cannot be considered a "simple bugfix" anymore and I'd rather prefer to send it to net-next with a later pull request.

This patch instead fixes the same problem but in a much simpler way (does not use of eth_hdr()).

I sent it over the ml for peer review. If nobody has any objection I will send it to net.

@Linus: I'd like to add your signed-off to this patch because it is essentially your patch but just reworked a bit. Please let me know what you think.

Cheers,

net/batman-adv/send.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c index 579f5f0..2f378a1 100644 --- a/net/batman-adv/send.c +++ b/net/batman-adv/send.c @@ -254,9 +254,9 @@ static int batadv_send_skb_unicast(struct batadv_priv *bat_priv, struct batadv_orig_node *orig_node, unsigned short vid) { - struct ethhdr *ethhdr = (struct ethhdr *)skb->data; + struct ethhdr *ethhdr; struct batadv_unicast_packet *unicast_packet; - int ret = NET_XMIT_DROP; + int ret = NET_XMIT_DROP, hdr_size;

if (!orig_node) goto out; @@ -265,12 +265,16 @@ static int batadv_send_skb_unicast(struct batadv_priv *bat_priv, case BATADV_UNICAST: if (!batadv_send_skb_prepare_unicast(skb, orig_node)) goto out; + + hdr_size = sizeof(*unicast_packet); break; case BATADV_UNICAST_4ADDR: if (!batadv_send_skb_prepare_unicast_4addr(bat_priv, skb, orig_node, packet_subtype)) goto out; + + hdr_size = sizeof(struct batadv_unicast_packet_4addr); break; default: /* this function supports UNICAST and UNICAST_4ADDR only. It @@ -279,6 +283,7 @@ static int batadv_send_skb_unicast(struct batadv_priv *bat_priv, goto out; }

+ eth_hdr = (struct eth_hdr *)(skb->data + hdr_size); unicast_packet = (struct batadv_unicast_packet *)skb->data;

/* inform the destination node that we are still missing a correct route