netfilter: Replace zero-length array with flexible-array member

[ Upstream commit 6daf14140129d30207ed6a0a69851fa6a3636bda ]

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

Lastly, fix checkpatch.pl warning
WARNING: __aligned(size) is preferred over __attribute__((aligned(size)))
in net/bridge/netfilter/ebtables.c

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Stable-dep-of: 542ed8145e6f ("netfilter: nft_set_hash: unaligned atomic read on struct nft_set_ext")
Signed-off-by: Sasha Levin <sashal@kernel.org>

11 files changed, 16 insertions, 16 deletions

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index f6853fc0fcc0..9d07cf277759 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1581,7 +1581,7 @@ struct compat_ebt_entry_mwt {
 		compat_uptr_t ptr;
 	} u;
 	compat_uint_t match_size;
-	compat_uint_t data[0] __attribute__ ((aligned (__alignof__(struct compat_ebt_replace))));
+	compat_uint_t data[] __aligned(__alignof__(struct compat_ebt_replace));
 };
 
 /* account for possible padding between match_size and ->data */
diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index a6f2e5bf7045..c62c9713e7dd 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -1057,7 +1057,7 @@ struct compat_arpt_replace {
 	u32				underflow[NF_ARP_NUMHOOKS];
 	u32				num_counters;
 	compat_uptr_t			counters;
-	struct compat_arpt_entry	entries[0];
+	struct compat_arpt_entry	entries[];
 };
 
 static inline void compat_release_entry(struct compat_arpt_entry *e)
@@ -1385,7 +1385,7 @@ static int compat_copy_entries_to_user(unsigned int total_size,
 struct compat_arpt_get_entries {
 	char name[XT_TABLE_MAXNAMELEN];
 	compat_uint_t size;
-	struct compat_arpt_entry entrytable[0];
+	struct compat_arpt_entry entrytable[];
 };
 
 static int compat_get_entries(struct net *net,
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 0076449eea35..c21ba5e62fff 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -1211,7 +1211,7 @@ struct compat_ipt_replace {
 	u32			underflow[NF_INET_NUMHOOKS];
 	u32			num_counters;
 	compat_uptr_t		counters;	/* struct xt_counters * */
-	struct compat_ipt_entry	entries[0];
+	struct compat_ipt_entry	entries[];
 };
 
 static int
@@ -1564,7 +1564,7 @@ compat_do_ipt_set_ctl(struct sock *sk,	int cmd, void __user *user,
 struct compat_ipt_get_entries {
 	char name[XT_TABLE_MAXNAMELEN];
 	compat_uint_t size;
-	struct compat_ipt_entry entrytable[0];
+	struct compat_ipt_entry entrytable[];
 };
 
 static int
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 41268612bdd4..010a70402828 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -1228,7 +1228,7 @@ struct compat_ip6t_replace {
 	u32			underflow[NF_INET_NUMHOOKS];
 	u32			num_counters;
 	compat_uptr_t		counters;	/* struct xt_counters * */
-	struct compat_ip6t_entry entries[0];
+	struct compat_ip6t_entry entries[];
 };
 
 static int
@@ -1574,7 +1574,7 @@ compat_do_ip6t_set_ctl(struct sock *sk, int cmd, void __user *user,
 struct compat_ip6t_get_entries {
 	char name[XT_TABLE_MAXNAMELEN];
 	compat_uint_t size;
-	struct compat_ip6t_entry entrytable[0];
+	struct compat_ip6t_entry entrytable[];
 };
 
 static int
diff --git a/net/netfilter/ipset/ip_set_bitmap_ip.c b/net/netfilter/ipset/ip_set_bitmap_ip.c
index e758b8120020..8fb170c7327f 100644
--- a/net/netfilter/ipset/ip_set_bitmap_ip.c
+++ b/net/netfilter/ipset/ip_set_bitmap_ip.c
@@ -46,7 +46,7 @@ struct bitmap_ip {
 	u8 netmask;		/* subnet netmask */
 	struct timer_list gc;	/* garbage collection */
 	struct ip_set *set;	/* attached to this ip_set */
-	unsigned char extensions[0]	/* data extensions */
+	unsigned char extensions[]	/* data extensions */
 		__aligned(__alignof__(u64));
 };
 
diff --git a/net/netfilter/ipset/ip_set_bitmap_ipmac.c b/net/netfilter/ipset/ip_set_bitmap_ipmac.c
index ae7cdc0d0f29..ebbcb9a16fe9 100644
--- a/net/netfilter/ipset/ip_set_bitmap_ipmac.c
+++ b/net/netfilter/ipset/ip_set_bitmap_ipmac.c
@@ -49,7 +49,7 @@ struct bitmap_ipmac {
 	size_t memsize;		/* members size */
 	struct timer_list gc;	/* garbage collector */
 	struct ip_set *set;	/* attached to this ip_set */
-	unsigned char extensions[0]	/* MAC + data extensions */
+	unsigned char extensions[]	/* MAC + data extensions */
 		__aligned(__alignof__(u64));
 };
 
diff --git a/net/netfilter/ipset/ip_set_bitmap_port.c b/net/netfilter/ipset/ip_set_bitmap_port.c
index d4a14750f5c4..1993f2783774 100644
--- a/net/netfilter/ipset/ip_set_bitmap_port.c
+++ b/net/netfilter/ipset/ip_set_bitmap_port.c
@@ -37,7 +37,7 @@ struct bitmap_port {
 	size_t memsize;		/* members size */
 	struct timer_list gc;	/* garbage collection */
 	struct ip_set *set;	/* attached to this ip_set */
-	unsigned char extensions[0]	/* data extensions */
+	unsigned char extensions[]	/* data extensions */
 		__aligned(__alignof__(u64));
 };
 
diff --git a/net/netfilter/ipset/ip_set_hash_gen.h b/net/netfilter/ipset/ip_set_hash_gen.h
index 4346cae25a4a..30b8b3fad150 100644
--- a/net/netfilter/ipset/ip_set_hash_gen.h
+++ b/net/netfilter/ipset/ip_set_hash_gen.h
@@ -76,7 +76,7 @@ struct hbucket {
 	DECLARE_BITMAP(used, AHASH_MAX_TUNED);
 	u8 size;		/* size of the array */
 	u8 pos;			/* position of the first free entry */
-	unsigned char value[0]	/* the array of the values */
+	unsigned char value[]	/* the array of the values */
 		__aligned(__alignof__(u64));
 };
 
@@ -109,7 +109,7 @@ struct htable {
 	u8 htable_bits;		/* size of hash table == 2^htable_bits */
 	u32 maxelem;		/* Maxelem per region */
 	struct ip_set_region *hregion;	/* Region locks and ext sizes */
-	struct hbucket __rcu *bucket[0]; /* hashtable buckets */
+	struct hbucket __rcu *bucket[]; /* hashtable buckets */
 };
 
 #define hbucket(h, i)		((h)->bucket[i])
diff --git a/net/netfilter/nfnetlink_acct.c b/net/netfilter/nfnetlink_acct.c
index 4b46421c5e17..ed4bde3c8850 100644
--- a/net/netfilter/nfnetlink_acct.c
+++ b/net/netfilter/nfnetlink_acct.c
@@ -33,7 +33,7 @@ struct nf_acct {
 	refcount_t		refcnt;
 	char			name[NFACCT_NAME_MAX];
 	struct rcu_head		rcu_head;
-	char			data[0];
+	char			data[];
 };
 
 struct nfacct_filter {
diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 8c835ad63729..9c5cfd74a0ee 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -132,7 +132,7 @@ struct xt_hashlimit_htable {
 	const char *name;
 	struct net *net;
 
-	struct hlist_head hash[0];	/* hashtable itself */
+	struct hlist_head hash[];	/* hashtable itself */
 };
 
 static int
diff --git a/net/netfilter/xt_recent.c b/net/netfilter/xt_recent.c
index 6fc0deb11aff..dae284e0ed15 100644
--- a/net/netfilter/xt_recent.c
+++ b/net/netfilter/xt_recent.c
@@ -71,7 +71,7 @@ struct recent_entry {
 	u_int8_t		ttl;
 	u_int8_t		index;
 	u_int16_t		nstamps;
-	unsigned long		stamps[0];
+	unsigned long		stamps[];
 };
 
 struct recent_table {
@@ -82,7 +82,7 @@ struct recent_table {
 	unsigned int		entries;
 	u8			nstamps_max_mask;
 	struct list_head	lru_list;
-	struct list_head	iphash[0];
+	struct list_head	iphash[];
 };
 
 struct recent_net {