Re: [PATCH] net/ipv4/ip_fragment:fix missing Flags reserved bit set in iphdr

[kernel test robot <lkp@intel.com>]

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Hi meijusan,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on ipvs/master]
[also build test WARNING on linus/master sparc-next/master v5.12 next-20210505]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/meijusan/net-ipv4-ip_fragment-fix-missing-Flags-reserved-bit-set-in-iphdr/20210505-212826
base:   https://git.kernel.org/pub/scm/linux/kernel/git/horms/ipvs.git master
config: x86_64-randconfig-a014-20210505 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 8f5a2a5836cc8e4c1def2bdeb022e7b496623439)
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 x86_64 cross compiling tool for clang build
        # apt-get install binutils-x86-64-linux-gnu
        # https://github.com/0day-ci/linux/commit/c6cde148fcd3bfdfa4ce7beac56893165236fd4e
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review meijusan/net-ipv4-ip_fragment-fix-missing-Flags-reserved-bit-set-in-iphdr/20210505-212826
        git checkout c6cde148fcd3bfdfa4ce7beac56893165236fd4e
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=x86_64 

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

All warnings (new ones prefixed by >>):

>> net/ipv4/ip_output.c:644:6: warning: variable 'ip_evil' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
           if (ntohs(iph->frag_off) & IP_EVIL)
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/byteorder/generic.h:142:18: note: expanded from macro 'ntohs'
   #define ntohs(x) ___ntohs(x)
                    ^
   include/linux/byteorder/generic.h:137:21: note: expanded from macro '___ntohs'
   #define ___ntohs(x) __be16_to_cpu(x)
                       ^
   include/uapi/linux/byteorder/little_endian.h:42:26: note: expanded from macro '__be16_to_cpu'
   #define __be16_to_cpu(x) __swab16((__force __u16)(__be16)(x))
                            ^
   include/uapi/linux/swab.h:102:21: note: expanded from macro '__swab16'
   #define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
                       ^
   net/ipv4/ip_output.c:655:6: note: uninitialized use occurs here
           if (ip_evil)
               ^~~~~~~
   net/ipv4/ip_output.c:644:2: note: remove the 'if' if its condition is always true
           if (ntohs(iph->frag_off) & IP_EVIL)
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   net/ipv4/ip_output.c:636:14: note: initialize the variable 'ip_evil' to silence this warning
           bool ip_evil;
                       ^
                        = 0
   1 warning generated.


vim +644 net/ipv4/ip_output.c

   630	
   631	void ip_fraglist_prepare(struct sk_buff *skb, struct ip_fraglist_iter *iter)
   632	{
   633		unsigned int hlen = iter->hlen;
   634		struct iphdr *iph = iter->iph;
   635		struct sk_buff *frag;
   636		bool ip_evil;
   637	
   638		frag = iter->frag;
   639		frag->ip_summed = CHECKSUM_NONE;
   640		skb_reset_transport_header(frag);
   641		__skb_push(frag, hlen);
   642		skb_reset_network_header(frag);
   643		memcpy(skb_network_header(frag), iph, hlen);
 > 644		if (ntohs(iph->frag_off) & IP_EVIL)
   645			ip_evil = true;
   646		iter->iph = ip_hdr(frag);
   647		iph = iter->iph;
   648		iph->tot_len = htons(frag->len);
   649		ip_copy_metadata(frag, skb);
   650		iter->offset += skb->len - hlen;
   651		iph->frag_off = htons(iter->offset >> 3);
   652		if (frag->next)
   653			iph->frag_off |= htons(IP_MF);
   654	
   655		if (ip_evil)
   656			iph->frag_off |= htons(IP_EVIL);
   657	
   658		/* Ready, complete checksum */
   659		ip_send_check(iph);
   660	}
   661	EXPORT_SYMBOL(ip_fraglist_prepare);
   662	

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

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