From 1259055170287a350cad453e9eac139c81609860 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= Date: Thu, 15 Mar 2018 08:29:09 +0100 Subject: [PATCH] brcmfmac: drop Inter-Access Point Protocol packets by default MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Testing brcmfmac with more recent firmwares resulted in AP interfaces not working in some specific setups. Debugging resulted in discovering support for IAPP in Broadcom's firmwares. Older firmwares were only generating 802.11f frames. Newer ones like: 1) 10.10 (TOB) (r663589) 2) 10.10.122.20 (r683106) for 4366b1 and 4366c0 respectively seem to also /respect/ 802.11f frames in the Tx path by performing a STA disassociation. This obsoleted standard and its implementation is something that: 1) Most people don't need / want to use 2) Can allow local DoS attacks 3) Breaks AP interfaces in some specific bridge setups To solve issues it can cause this commit modifies brcmfmac to drop IAPP packets. If affects: 1) Rx path: driver won't be sending these unwanted packets up. 2) Tx path: driver will reject packets that would trigger STA disassociation perfromed by a firmware (possible local DoS attack). It appears there are some Broadcom's clients/users who care about this feature despite the drawbacks. They can switch it on using a new module param. This change results in only two more comparisons (check for module param and check for Ethernet packet length) for 99.9% of packets. Its overhead should be very minimal. Signed-off-by: Rafał Miłecki Acked-by: Arend van Spriel Signed-off-by: Kalle Valo --- .../wireless/broadcom/brcm80211/brcmfmac/common.c | 5 ++ .../wireless/broadcom/brcm80211/brcmfmac/common.h | 1 + .../wireless/broadcom/brcm80211/brcmfmac/core.c | 57 ++++++++++++++++++++++ 3 files changed, 63 insertions(+) --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/common.c +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/common.c @@ -75,6 +75,10 @@ static int brcmf_roamoff; module_param_named(roamoff, brcmf_roamoff, int, S_IRUSR); MODULE_PARM_DESC(roamoff, "Do not use internal roaming engine"); +static int brcmf_iapp_enable; +module_param_named(iapp, brcmf_iapp_enable, int, 0); +MODULE_PARM_DESC(iapp, "Enable partial support for the obsoleted Inter-Access Point Protocol"); + #ifdef DEBUG /* always succeed brcmf_bus_started() */ static int brcmf_ignore_probe_fail; @@ -441,6 +445,7 @@ struct brcmf_mp_device *brcmf_get_module settings->feature_disable = brcmf_feature_disable; settings->fcmode = brcmf_fcmode; settings->roamoff = !!brcmf_roamoff; + settings->iapp = !!brcmf_iapp_enable; #ifdef DEBUG settings->ignore_probe_fail = !!brcmf_ignore_probe_fail; #endif --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/common.h +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/common.h @@ -58,6 +58,7 @@ struct brcmf_mp_device { unsigned int feature_disable; int fcmode; bool roamoff; + bool iapp; bool ignore_probe_fail; struct brcmfmac_pd_cc *country_codes; union { --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c @@ -230,6 +230,37 @@ static void brcmf_netdev_set_multicast_l schedule_work(&ifp->multicast_work); } +/** + * brcmf_skb_is_iapp - checks if skb is an IAPP packet + * + * @skb: skb to check + */ +static bool brcmf_skb_is_iapp(struct sk_buff *skb) +{ + static const u8 iapp_l2_update_packet[6] __aligned(2) = { + 0x00, 0x01, 0xaf, 0x81, 0x01, 0x00, + }; + unsigned char *eth_data; +#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) + const u16 *a, *b; +#endif + + if (skb->len - skb->mac_len != 6 || + !is_multicast_ether_addr(eth_hdr(skb)->h_dest)) + return false; + + eth_data = skb_mac_header(skb) + ETH_HLEN; +#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) + return !(((*(const u32 *)eth_data) ^ (*(const u32 *)iapp_l2_update_packet)) | + ((*(const u16 *)(eth_data + 4)) ^ (*(const u16 *)(iapp_l2_update_packet + 4)))); +#else + a = (const u16 *)eth_data; + b = (const u16 *)iapp_l2_update_packet; + + return !((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2])); +#endif +} + static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb, struct net_device *ndev) { @@ -250,6 +281,23 @@ static netdev_tx_t brcmf_netdev_start_xm goto done; } + /* Some recent Broadcom's firmwares disassociate STA when they receive + * an 802.11f ADD frame. This behavior can lead to a local DoS security + * issue. Attacker may trigger disassociation of any STA by sending a + * proper Ethernet frame to the wireless interface. + * + * Moreover this feature may break AP interfaces in some specific + * setups. This applies e.g. to the bridge with hairpin mode enabled and + * IFLA_BRPORT_MCAST_TO_UCAST set. IAPP packet generated by a firmware + * will get passed back to the wireless interface and cause immediate + * disassociation of a just-connected STA. + */ + if (!drvr->settings->iapp && brcmf_skb_is_iapp(skb)) { + dev_kfree_skb(skb); + ret = -EINVAL; + goto done; + } + /* Make sure there's enough writeable headroom */ if (skb_headroom(skb) < drvr->hdrlen || skb_header_cloned(skb)) { head_delta = max_t(int, drvr->hdrlen - skb_headroom(skb), 0); @@ -325,6 +373,15 @@ void brcmf_txflowblock_if(struct brcmf_i void brcmf_netif_rx(struct brcmf_if *ifp, struct sk_buff *skb) { + /* Most of Broadcom's firmwares send 802.11f ADD frame every time a new + * STA connects to the AP interface. This is an obsoleted standard most + * users don't use, so don't pass these frames up unless requested. + */ + if (!ifp->drvr->settings->iapp && brcmf_skb_is_iapp(skb)) { + brcmu_pkt_buf_free_skb(skb); + return; + } + if (skb->pkt_type == PACKET_MULTICAST) ifp->ndev->stats.multicast++;