tipc: handle the err returned from cmd header function

Syzbot found a crash:

  BUG: KMSAN: uninit-value in tipc_nl_compat_name_table_dump+0x54f/0xcd0 net/tipc/netlink_compat.c:872
  Call Trace:
    tipc_nl_compat_name_table_dump+0x54f/0xcd0 net/tipc/netlink_compat.c:872
    __tipc_nl_compat_dumpit+0x59e/0xda0 net/tipc/netlink_compat.c:215
    tipc_nl_compat_dumpit+0x63a/0x820 net/tipc/netlink_compat.c:280
    tipc_nl_compat_handle net/tipc/netlink_compat.c:1226 [inline]
    tipc_nl_compat_recv+0x1b5f/0x2750 net/tipc/netlink_compat.c:1265
    genl_family_rcv_msg net/netlink/genetlink.c:601 [inline]
    genl_rcv_msg+0x185f/0x1a60 net/netlink/genetlink.c:626
    netlink_rcv_skb+0x431/0x620 net/netlink/af_netlink.c:2477
    genl_rcv+0x63/0x80 net/netlink/genetlink.c:637
    netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
    netlink_unicast+0xf3e/0x1020 net/netlink/af_netlink.c:1336
    netlink_sendmsg+0x127f/0x1300 net/netlink/af_netlink.c:1917
    sock_sendmsg_nosec net/socket.c:622 [inline]
    sock_sendmsg net/socket.c:632 [inline]

  Uninit was created at:
    __alloc_skb+0x309/0xa20 net/core/skbuff.c:208
    alloc_skb include/linux/skbuff.h:1012 [inline]
    netlink_alloc_large_skb net/netlink/af_netlink.c:1182 [inline]
    netlink_sendmsg+0xb82/0x1300 net/netlink/af_netlink.c:1892
    sock_sendmsg_nosec net/socket.c:622 [inline]
    sock_sendmsg net/socket.c:632 [inline]

It was supposed to be fixed on commit 974cb0e3 ("tipc: fix uninit-value
in tipc_nl_compat_name_table_dump") by checking TLV_GET_DATA_LEN(msg->req)
in cmd->header()/tipc_nl_compat_name_table_dump_header(), which is called
ahead of tipc_nl_compat_name_table_dump().

However, tipc_nl_compat_dumpit() doesn't handle the error returned from cmd
header function. It means even when the check added in that fix fails, it
won't stop calling tipc_nl_compat_name_table_dump(), and the issue will be
triggered again.

So this patch is to add the process for the err returned from cmd header
function in tipc_nl_compat_dumpit().

Reported-by: syzbot+3ce8520484b0d4e260a5@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/netlink_compat.c

@@ -267,8 +267,14 @@ static int tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
 	if (msg->rep_type)
 		tipc_tlv_init(msg->rep, msg->rep_type);
 
-	if (cmd->header)
-		(*cmd->header)(msg);
+	if (cmd->header) {
+		err = (*cmd->header)(msg);
+		if (err) {
+			kfree_skb(msg->rep);
+			msg->rep = NULL;
+			return err;
+		}
+	}
 
 	arg = nlmsg_new(0, GFP_KERNEL);
 	if (!arg) {