vxlan: Fix uninit-value in vxlan_vnifilter_dump()

KMSAN reported an uninit-value access in vxlan_vnifilter_dump() [1].

If the length of the netlink message payload is less than
sizeof(struct tunnel_msg), vxlan_vnifilter_dump() accesses bytes
beyond the message. This can lead to uninit-value access. Fix this by
returning an error in such situations.

[1]
BUG: KMSAN: uninit-value in vxlan_vnifilter_dump+0x328/0x920 drivers/net/vxlan/vxlan_vnifilter.c:422
 vxlan_vnifilter_dump+0x328/0x920 drivers/net/vxlan/vxlan_vnifilter.c:422
 rtnl_dumpit+0xd5/0x2f0 net/core/rtnetlink.c:6786
 netlink_dump+0x93e/0x15f0 net/netlink/af_netlink.c:2317
 __netlink_dump_start+0x716/0xd60 net/netlink/af_netlink.c:2432
 netlink_dump_start include/linux/netlink.h:340 [inline]
 rtnetlink_dump_start net/core/rtnetlink.c:6815 [inline]
 rtnetlink_rcv_msg+0x1256/0x14a0 net/core/rtnetlink.c:6882
 netlink_rcv_skb+0x467/0x660 net/netlink/af_netlink.c:2542
 rtnetlink_rcv+0x35/0x40 net/core/rtnetlink.c:6944
 netlink_unicast_kernel net/netlink/af_netlink.c:1321 [inline]
 netlink_unicast+0xed6/0x1290 net/netlink/af_netlink.c:1347
 netlink_sendmsg+0x1092/0x1230 net/netlink/af_netlink.c:1891
 sock_sendmsg_nosec net/socket.c:711 [inline]
 __sock_sendmsg+0x330/0x3d0 net/socket.c:726
 ____sys_sendmsg+0x7f4/0xb50 net/socket.c:2583
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2637
 __sys_sendmsg net/socket.c:2669 [inline]
 __do_sys_sendmsg net/socket.c:2674 [inline]
 __se_sys_sendmsg net/socket.c:2672 [inline]
 __x64_sys_sendmsg+0x211/0x3e0 net/socket.c:2672
 x64_sys_call+0x3878/0x3d90 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xd9/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4110 [inline]
 slab_alloc_node mm/slub.c:4153 [inline]
 kmem_cache_alloc_node_noprof+0x800/0xe80 mm/slub.c:4205
 kmalloc_reserve+0x13b/0x4b0 net/core/skbuff.c:587
 __alloc_skb+0x347/0x7d0 net/core/skbuff.c:678
 alloc_skb include/linux/skbuff.h:1323 [inline]
 netlink_alloc_large_skb+0xa5/0x280 net/netlink/af_netlink.c:1196
 netlink_sendmsg+0xac9/0x1230 net/netlink/af_netlink.c:1866
 sock_sendmsg_nosec net/socket.c:711 [inline]
 __sock_sendmsg+0x330/0x3d0 net/socket.c:726
 ____sys_sendmsg+0x7f4/0xb50 net/socket.c:2583
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2637
 __sys_sendmsg net/socket.c:2669 [inline]
 __do_sys_sendmsg net/socket.c:2674 [inline]
 __se_sys_sendmsg net/socket.c:2672 [inline]
 __x64_sys_sendmsg+0x211/0x3e0 net/socket.c:2672
 x64_sys_call+0x3878/0x3d90 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xd9/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 0 UID: 0 PID: 30991 Comm: syz.4.10630 Not tainted 6.12.0-10694-gc44daa7e3c73 #29
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014

Fixes: f9c4bb0 ("vxlan: vni filtering support on collect metadata device")
Reported-by: syzkaller <[email protected]>
Signed-off-by: Shigeru Yoshida <[email protected]>
Reviewed-by: Ido Schimmel <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Shigeru Yoshida

drivers/net/vxlan/vxlan_vnifilter.c

@@ -411,6 +411,11 @@ static int vxlan_vnifilter_dump(struct sk_buff *skb, struct netlink_callback *cb
 	struct tunnel_msg *tmsg;
 	struct net_device *dev;
 
+	if (cb->nlh->nlmsg_len < nlmsg_msg_size(sizeof(struct tunnel_msg))) {
+		NL_SET_ERR_MSG(cb->extack, "Invalid msg length");
+		return -EINVAL;
+	}
+
 	tmsg = nlmsg_data(cb->nlh);
 
 	if (tmsg->flags & ~TUNNEL_MSG_VALID_USER_FLAGS) {