Re: [PATCH net] net: prevent NULL pointer dereference in rt_fibinfo_free() and rt_fibinfo_free_cpus()

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

Hi Jeongjun,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Jeongjun-Park/net-prevent-NULL-pointer-dereference-in-rt_fibinfo_free-and-rt_fibinfo_free_cpus/20240910-025008
base:   net/main
patch link:    https://lore.kernel.org/r/20240909184827.123071-1-aha310510%40gmail.com
patch subject: [PATCH net] net: prevent NULL pointer dereference in rt_fibinfo_free() and rt_fibinfo_free_cpus()
config: arc-randconfig-002-20240910 (https://download.01.org/0day-ci/archive/20240910/202409102210.krjQJVRr-lkp@intel.com/config)
compiler: arc-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240910/202409102210.krjQJVRr-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409102210.krjQJVRr-lkp@intel.com/

All warnings (new ones prefixed by >>):

   net/ipv4/fib_semantics.c: In function 'rt_fibinfo_free':
>> net/ipv4/fib_semantics.c:156:13: warning: the comparison will always evaluate as 'true' for the address of 'dst' will never be NULL [-Waddress]
     156 |         if (!&rt->dst)
         |             ^
   In file included from include/net/ip.h:30,
                    from net/ipv4/fib_semantics.c:37:
   include/net/route.h:56:33: note: 'dst' declared here
      56 |         struct dst_entry        dst;
         |                                 ^~~
   net/ipv4/fib_semantics.c: In function 'rt_fibinfo_free_cpus':
   net/ipv4/fib_semantics.c:209:21: warning: the comparison will always evaluate as 'true' for the address of 'dst' will never be NULL [-Waddress]
     209 |                 if (!&rt->dst)
         |                     ^
   include/net/route.h:56:33: note: 'dst' declared here
      56 |         struct dst_entry        dst;
         |                                 ^~~


vim +156 net/ipv4/fib_semantics.c

   149	
   150	static void rt_fibinfo_free(struct rtable __rcu **rtp)
   151	{
   152		struct rtable *rt = rcu_dereference_protected(*rtp, 1);
   153	
   154		if (!rt)
   155			return;
 > 156		if (!&rt->dst)
   157			return;
   158	
   159		/* Not even needed : RCU_INIT_POINTER(*rtp, NULL);
   160		 * because we waited an RCU grace period before calling
   161		 * free_fib_info_rcu()
   162		 */
   163	
   164		dst_dev_put(&rt->dst);
   165		dst_release_immediate(&rt->dst);
   166	}
   167	

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