From cbb11d3293ec8c61da4a44d158a8693237a9d3c0 Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Mon, 16 Dec 2024 15:42:07 +0200 Subject: [PATCH] vxlan: Avoid accessing uninitialized memory during xmit The VXLAN driver does not verify that transmitted packets have an Ethernet header in the linear part of the skb, which can result in the driver accessing uninitialized memory while processing the Ethernet header [1]. Issue can be reproduced using [2]. Fix by checking that we can pull the Ethernet header into the linear part of the skb. Note that the driver can transmit IP packets, but this is handled earlier in the xmit path. [1] CPU: 6 UID: 0 PID: 404 Comm: bpftool Tainted: G B 6.12.0-rc7-custom-g10d3437464d3 #232 Tainted: [B]=BAD_PAGE Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-2.fc40 04/01/2014 ===================================================== ===================================================== BUG: KMSAN: uninit-value in __vxlan_find_mac+0x449/0x450 __vxlan_find_mac+0x449/0x450 vxlan_xmit+0x1265/0x2f70 dev_hard_start_xmit+0x239/0x7e0 __dev_queue_xmit+0x2d65/0x45e0 __bpf_redirect+0x6d2/0xf60 bpf_clone_redirect+0x2c7/0x450 bpf_prog_7423975f9f8be99f_mac_repo+0x20/0x22 bpf_test_run+0x60f/0xca0 bpf_prog_test_run_skb+0x115d/0x2300 bpf_prog_test_run+0x3b3/0x5c0 __sys_bpf+0x501/0xc60 __x64_sys_bpf+0xa8/0xf0 do_syscall_64+0xd9/0x1b0 entry_SYSCALL_64_after_hwframe+0x77/0x7f Uninit was stored to memory at: __vxlan_find_mac+0x442/0x450 vxlan_xmit+0x1265/0x2f70 dev_hard_start_xmit+0x239/0x7e0 __dev_queue_xmit+0x2d65/0x45e0 __bpf_redirect+0x6d2/0xf60 bpf_clone_redirect+0x2c7/0x450 bpf_prog_7423975f9f8be99f_mac_repo+0x20/0x22 bpf_test_run+0x60f/0xca0 bpf_prog_test_run_skb+0x115d/0x2300 bpf_prog_test_run+0x3b3/0x5c0 __sys_bpf+0x501/0xc60 __x64_sys_bpf+0xa8/0xf0 do_syscall_64+0xd9/0x1b0 entry_SYSCALL_64_after_hwframe+0x77/0x7f Uninit was created at: kmem_cache_alloc_node_noprof+0x4a8/0x9e0 kmalloc_reserve+0xd1/0x420 pskb_expand_head+0x1b4/0x15f0 skb_ensure_writable+0x2ee/0x390 bpf_clone_redirect+0x16a/0x450 bpf_prog_7423975f9f8be99f_mac_repo+0x20/0x22 bpf_test_run+0x60f/0xca0 bpf_prog_test_run_skb+0x115d/0x2300 bpf_prog_test_run+0x3b3/0x5c0 __sys_bpf+0x501/0xc60 __x64_sys_bpf+0xa8/0xf0 do_syscall_64+0xd9/0x1b0 [2] $ cat mac_repo.bpf.c // SPDX-License-Identifier: GPL-2.0 #include #include SEC("lwt_xmit") int mac_repo(struct __sk_buff *skb) { return bpf_clone_redirect(skb, 100, 0); } $ clang -O2 -target bpf -c mac_repo.bpf.c -o mac_repo.o # ip link add name vx0 up index 100 type vxlan id 10010 dstport 4789 local 192.0.2.1 # bpftool prog load mac_repo.o /sys/fs/bpf/mac_repo # echo -ne "\x41\x41\x41\x41\x41\x41\x41\x41\x41\x41\x41\x41\x41\x41\x41" | \ bpftool prog run pinned /sys/fs/bpf/mac_repo data_in - repeat 10 Fixes: d342894c5d2f ("vxlan: virtual extensible lan") Reported-by: syzbot+35e7e2811bbe5777b20e@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6735d39a.050a0220.1324f8.0096.GAE@google.com/ Signed-off-by: Ido Schimmel Signed-off-by: NipaLocal --- drivers/net/vxlan/vxlan_core.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c index 0c356e0a61ef01..f409c5e974f02e 100644 --- a/drivers/net/vxlan/vxlan_core.c +++ b/drivers/net/vxlan/vxlan_core.c @@ -2716,6 +2716,7 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev) struct vxlan_dev *vxlan = netdev_priv(dev); struct vxlan_rdst *rdst, *fdst = NULL; const struct ip_tunnel_info *info; + enum skb_drop_reason reason; struct vxlan_fdb *f; struct ethhdr *eth; __be32 vni = 0; @@ -2740,6 +2741,15 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev) } } + reason = pskb_may_pull_reason(skb, ETH_HLEN); + if (unlikely(reason != SKB_NOT_DROPPED_YET)) { + dev_core_stats_tx_dropped_inc(dev); + vxlan_vnifilter_count(vxlan, vni, NULL, + VXLAN_VNI_STATS_TX_DROPS, 0); + kfree_skb_reason(skb, reason); + return NETDEV_TX_OK; + } + if (vxlan->cfg.flags & VXLAN_F_PROXY) { eth = eth_hdr(skb); if (ntohs(eth->h_proto) == ETH_P_ARP)