[nf,2/2] netfilter: nft_osf: check for TCP packet before further processing

The osf expression only supports for TCP packets, add a upfront sanity
check to skip packet parsing if this is not a TCP packet.

Fixes: b96af92d6eaf ("netfilter: nf_tables: implement Passive OS fingerprint module in nft_osf")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nft_osf.c | 5 +++++
 1 file changed, 5 insertions(+)

Hi Pablo,

I love your patch! Yet something to improve:

[auto build test ERROR on nf/master]

url:    https://github.com/0day-ci/linux/commits/Pablo-Neira-Ayuso/netfilter-nft_exthdr-check-for-IPv6-packet-before-further-processing/20210616-144640
base:   https://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf.git master
config: arm-randconfig-r001-20210615 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 64720f57bea6a6bf033feef4a5751ab9c0c3b401)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install arm cross compiling tool for clang build
        # apt-get install binutils-arm-linux-gnueabi
        # https://github.com/0day-ci/linux/commit/f572a05becf9cc86053b01e0f0f898334583692a
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Pablo-Neira-Ayuso/netfilter-nft_exthdr-check-for-IPv6-packet-before-further-processing/20210616-144640
        git checkout f572a05becf9cc86053b01e0f0f898334583692a
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> net/netfilter/nft_osf.c:33:3: error: 'break' statement not in loop or switch statement
                   break;
                   ^
   1 error generated.


vim +/break +33 net/netfilter/nft_osf.c

    19	
    20	static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs,
    21				 const struct nft_pktinfo *pkt)
    22	{
    23		struct nft_osf *priv = nft_expr_priv(expr);
    24		u32 *dest = &regs->data[priv->dreg];
    25		struct sk_buff *skb = pkt->skb;
    26		char os_match[NFT_OSF_MAXGENRELEN + 1];
    27		const struct tcphdr *tcp;
    28		struct nf_osf_data data;
    29		struct tcphdr _tcph;
    30	
    31		if (pkt->tprot != IPPROTO_TCP) {
    32			regs->verdict.code = NFT_BREAK;
  > 33			break;
    34		}
    35	
    36		tcp = skb_header_pointer(skb, ip_hdrlen(skb),
    37					 sizeof(struct tcphdr), &_tcph);
    38		if (!tcp) {
    39			regs->verdict.code = NFT_BREAK;
    40			return;
    41		}
    42		if (!tcp->syn) {
    43			regs->verdict.code = NFT_BREAK;
    44			return;
    45		}
    46	
    47		if (!nf_osf_find(skb, nf_osf_fingers, priv->ttl, &data)) {
    48			strncpy((char *)dest, "unknown", NFT_OSF_MAXGENRELEN);
    49		} else {
    50			if (priv->flags & NFT_OSF_F_VERSION)
    51				snprintf(os_match, NFT_OSF_MAXGENRELEN, "%s:%s",
    52					 data.genre, data.version);
    53			else
    54				strlcpy(os_match, data.genre, NFT_OSF_MAXGENRELEN);
    55	
    56			strncpy((char *)dest, os_match, NFT_OSF_MAXGENRELEN);
    57		}
    58	}
    59	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org