netfilter: conntrack: avoid gcc-10 zero-length-bounds warning

[ Upstream commit 2c407aca64977ede9b9f35158e919773cae2082f ]

gcc-10 warns around a suspicious access to an empty struct member:

net/netfilter/nf_conntrack_core.c: In function '__nf_conntrack_alloc':
net/netfilter/nf_conntrack_core.c:1522:9: warning: array subscript 0 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[0]'} [-Wzero-length-bounds]
 1522 |  memset(&ct->__nfct_init_offset[0], 0,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from net/netfilter/nf_conntrack_core.c:37:
include/net/netfilter/nf_conntrack.h:90:5: note: while referencing '__nfct_init_offset'
   90 |  u8 __nfct_init_offset[0];
      |     ^~~~~~~~~~~~~~~~~~

The code is correct but a bit unusual. Rework it slightly in a way that
does not trigger the warning, using an empty struct instead of an empty
array. There are probably more elegant ways to do this, but this is the
smallest change.

Fixes: c41884ce0562 ("netfilter: conntrack: avoid zeroing timer")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index 636e9e11bd5f638a66d116f6fddcad3b299155e3..e3f73fd1d53a97ee57f8c3a5d9e42df596bc1fa2 100644 (file)
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -98,7 +98,7 @@ struct nf_conn {
        possible_net_t ct_net;
 
        /* all members below initialized via memset */
-       u8 __nfct_init_offset[0];
+       struct { } __nfct_init_offset;
 
        /* If we were expected by an expectation, this will be it */
        struct nf_conn *master;

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index de0aad12b91d26f33d1614b91a60868e3adf50fd..e58516274e86a118cdd9f86c73cea41573714653 100644 (file)
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -898,9 +898,9 @@ __nf_conntrack_alloc(struct net *net,
        /* Don't set timer yet: wait for confirmation */
        setup_timer(&ct->timeout, death_by_timeout, (unsigned long)ct);
        write_pnet(&ct->ct_net, net);
-       memset(&ct->__nfct_init_offset[0], 0,
+       memset(&ct->__nfct_init_offset, 0,
               offsetof(struct nf_conn, proto) -
-              offsetof(struct nf_conn, __nfct_init_offset[0]));
+              offsetof(struct nf_conn, __nfct_init_offset));
 
        if (zone && nf_ct_zone_add(ct, GFP_ATOMIC, zone) < 0)
                goto out_free;