tipc: fix uninit skb->data in tipc_nl_compat_dumpit()

__tipc_nl_compat_dumpit() has two callers, and it expects them to
pass a valid nlmsghdr via arg->data. This header is artificial and
crafted just for __tipc_nl_compat_dumpit().

tipc_nl_compat_publ_dump() does so by putting a genlmsghdr as well
as some nested attribute, TIPC_NLA_SOCK. But the other caller
tipc_nl_compat_dumpit() does not, this leaves arg->data uninitialized
on this call path.

Fix this by just adding a similar nlmsghdr without any payload in
tipc_nl_compat_dumpit().

This bug exists since day 1, but the recent commit 6ea67769ff33
("net: tipc: prepare attrs in __tipc_nl_compat_dumpit()") makes it
easier to appear.

Reported-and-tested-by: syzbot+0e7181deafa7e0b79923@syzkaller.appspotmail.com
Fixes: d0796d1ef63d ("tipc: convert legacy nl bearer dump to nl compat")
Cc: Jon Maloy <jmaloy@redhat.com>
Cc: Ying Xue <ying.xue@windriver.com>
Cc: Richard Alpe <richard.alpe@ericsson.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/tipc/netlink_compat.c b/net/tipc/netlink_compat.c
index 2175163..90e3c70 100644 (file)
--- a/net/tipc/netlink_compat.c
+++ b/net/tipc/netlink_compat.c
@@ -275,8 +275,9 @@ err_out:
 static int tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
                                 struct tipc_nl_compat_msg *msg)
 {
-       int err;
+       struct nlmsghdr *nlh;
        struct sk_buff *arg;
+       int err;
 
        if (msg->req_type && (!msg->req_size ||
                              !TLV_CHECK_TYPE(msg->req, msg->req_type)))
@@ -305,6 +306,15 @@ static int tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
                return -ENOMEM;
        }
 
+       nlh = nlmsg_put(arg, 0, 0, tipc_genl_family.id, 0, NLM_F_MULTI);
+       if (!nlh) {
+               kfree_skb(arg);
+               kfree_skb(msg->rep);
+               msg->rep = NULL;
+               return -EMSGSIZE;
+       }
+       nlmsg_end(arg, nlh);
+
        err = __tipc_nl_compat_dumpit(cmd, msg, arg);
        if (err) {
                kfree_skb(msg->rep);