Re: [PATCH] netfilter: ip_tables: remove useless variable assignment in get_info()

Hi Joe,

Quoting Joe Perches [off-list ref]:

On Mon, 2017-06-26 at 17:34 -0500, Gustavo A. R. Silva wrote:

quoted

Value assigned to variable _ret_ at line 970 is overwritten either at
line 986 or 988, before it can be used. This makes such variable
assignment useless.

Addresses-Coverity-ID: 1226932

[]

quoted

diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c

[]

quoted

@@ -967,7 +967,7 @@ static int get_info(struct net *net, void __user *user,
 		struct xt_table_info tmp;

 		if (compat) {
-			ret = compat_table_info(private, &tmp);
+			compat_table_info(private, &tmp);

why isn't it more appropriate to test the return value?

Oh, in this particular case, based on git blame, the code has been like that for more than 10 years. So my reasoning was that if it hasn't been fixed yet, maybe that return value is not relevant.

But in case it turns out to actually be relevant, what do you think about the following patch:

--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c

@@ -968,7 +968,8 @@ static int get_info(struct net *net, void __user *user,

                if (compat) {
                        ret = compat_table_info(private, &tmp);
-                       xt_compat_flush_offsets(AF_INET);
+                       if (!ret)
+                               goto out;
                        private = &tmp;
                }
 #endif

@@ -986,14 +987,20 @@ static int get_info(struct net *net, void __user *user,
                        ret = -EFAULT;
                else
                        ret = 0;
+       } else
+               ret = -ENOENT;

+out:
+       if (t) {
                xt_table_unlock(t);
                module_put(t->me);
-       } else
-               ret = -ENOENT;
+       }
+
 #ifdef CONFIG_COMPAT
-       if (compat)
+       if (compat) {
+               xt_compat_flush_offsets(AF_INET);
                xt_compat_unlock(AF_INET);
+       }
 #endif
        return ret;
 }

Thank you!
--
Gustavo A. R. Silva