Subject: Re: [PATCH net v5 1/2] net: netfilter: Limit the number of ftp helper port attempts

From: kernel test robot <[email-masked]>
Date: Mon, 20 Sep 2021 13:09:27 +0800

Hi Cole,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on net/master]

url:    https://github.com/0day-ci/linux/commits/Cole-Dishington/Fix-port-selection-of-FTP-for-NF_NAT_RANGE_PROTO_SPECIFIED/20210920-090056
base:   https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git e30cd812dffadc58241ae378e48728e6a161becd
config: i386-defconfig (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/b90b875dc5be3c59ec418ce403a8d749690a24ec
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Cole-Dishington/Fix-port-selection-of-FTP-for-NF_NAT_RANGE_PROTO_SPECIFIED/20210920-090056
        git checkout b90b875dc5be3c59ec418ce403a8d749690a24ec
        # save the attached .config to linux build tree
        make W=1 ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <[email-masked]>

All warnings (new ones prefixed by >>):

   net/netfilter/nf_nat_ftp.c: In function 'nf_nat_ftp':
>> net/netfilter/nf_nat_ftp.c:117:37: warning: format '%u' expects a matching 'unsigned int' argument [-Wformat=]
     117 |   nf_ct_helper_log(skb, ct, "tried %u ports, all were in use");
         |                                    ~^
         |                                     |
         |                                     unsigned int

vim +117 net/netfilter/nf_nat_ftp.c

    60	
    61	/* So, this packet has hit the connection tracking matching code.
    62	   Mangle it, and change the expectation to match the new version. */
    63	static unsigned int nf_nat_ftp(struct sk_buff *skb,
    64				       enum ip_conntrack_info ctinfo,
    65				       enum nf_ct_ftp_type type,
    66				       unsigned int protoff,
    67				       unsigned int matchoff,
    68				       unsigned int matchlen,
    69				       struct nf_conntrack_expect *exp)
    70	{
    71		union nf_inet_addr newaddr;
    72		u_int16_t port;
    73		int dir = CTINFO2DIR(ctinfo);
    74		struct nf_conn *ct = exp->master;
    75		unsigned int i, min, max, range_size;
    76		static const unsigned int max_attempts = 128;
    77		char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
    78		unsigned int buflen;
    79		int ret;
    80	
    81		pr_debug("type %i, off %u len %u\n", type, matchoff, matchlen);
    82	
    83		/* Connection will come from wherever this packet goes, hence !dir */
    84		newaddr = ct->tuplehash[!dir].tuple.dst.u3;
    85		exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
    86		exp->dir = !dir;
    87	
    88		/* When you see the packet, we need to NAT it the same as the
    89		 * this one. */
    90		exp->expectfn = nf_nat_follow_master;
    91	
    92		min = ntohs(exp->saved_proto.tcp.port);
    93		max = 65535;
    94	
    95		/* Try to get same port */
    96		ret = nf_ct_expect_related(exp, 0);
    97	
    98		/* if same port is not in range or available, try to change it. */
    99		if (ret != 0) {
   100			range_size = max - min + 1;
   101			if (range_size > max_attempts)
   102				range_size = max_attempts;
   103	
   104			port = min + prandom_u32_max(max - min);
   105			for (i = 0; i < range_size; i++) {
   106				exp->tuple.dst.u.tcp.port = htons(port);
   107				ret = nf_ct_expect_related(exp, 0);
   108				if (ret != -EBUSY)
   109					break;
   110				port++;
   111				if (port > max)
   112					port = min;
   113			}
   114		}
   115	
   116		if (ret != 0) {
 > 117			nf_ct_helper_log(skb, ct, "tried %u ports, all were in use");
   118			return NF_DROP;
   119		}
   120	
   121		buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
   122					    &newaddr, port);
   123		if (!buflen)
   124			goto out;
   125	
   126		pr_debug("calling nf_nat_mangle_tcp_packet\n");
   127	
   128		if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
   129					      matchlen, buffer, buflen))
   130			goto out;
   131	
   132		return NF_ACCEPT;
   133	
   134	out:
   135		nf_ct_helper_log(skb, ct, "cannot mangle packet");
   136		nf_ct_unexpect_related(exp);
   137		return NF_DROP;
   138	}
   139	

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