[PATCH] netfilter: fix stringop-overflow warning with UBSAN

[Arnd Bergmann]

Using gcc-7 with UBSAN enabled, we get this false-positive warning:

net/netfilter/ipset/ip_set_core.c: In function 'ip_set_sockfn_get':
net/netfilter/ipset/ip_set_core.c:1998:3: error: 'strncpy' writing 32 bytes 
into a region of size 2 overflows the destination [-Werror=stringop-overflow=]
   strncpy(req_get->set.name, set ? set->name : "",
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    sizeof(req_get->set.name));
    ~~~~~~~~~~~~~~~~~~~~~~~~~~

This seems completely bogus, and I could not find a nice workaround.
To work around it in a less elegant way, I change the ?: operator
into an if()/else() construct.

Signed-off-by: Arnd Bergmann <a...@arndb.de>
---
 net/netfilter/ipset/ip_set_core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_core.c 
b/net/netfilter/ipset/ip_set_core.c
index e495b5e484b1..d7ebb021003b 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -1995,8 +1995,12 @@ ip_set_sockfn_get(struct sock *sk, int optval, void 
__user *user, int *len)
                }
                nfnl_lock(NFNL_SUBSYS_IPSET);
                set = ip_set(inst, req_get->set.index);
-               strncpy(req_get->set.name, set ? set->name : "",
-                       IPSET_MAXNAMELEN);
+               if (set)
+                       strncpy(req_get->set.name, set->name,
+                               sizeof(req_get->set.name));
+               else
+                       memset(req_get->set.name, '\0',
+                              sizeof(req_get->set.name));
                nfnl_unlock(NFNL_SUBSYS_IPSET);
                goto copy;
        }
-- 
2.9.0