[PATCH][next] netfilter: Replace zero-length array with flexible-array member

From: Gustavo A. R. Silva
Date: Thu Feb 20 2020 - 08:56:37 EST

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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@xxxxxxxxxxxxxx>
---
include/linux/netfilter/ipset/ip_set.h | 2 +-
include/linux/netfilter/x_tables.h | 8 ++++----
include/linux/netfilter_arp/arp_tables.h | 2 +-
include/linux/netfilter_bridge/ebtables.h | 2 +-
include/linux/netfilter_ipv4/ip_tables.h | 2 +-
include/linux/netfilter_ipv6/ip6_tables.h | 2 +-
include/net/netfilter/nf_conntrack_extend.h | 2 +-
include/net/netfilter/nf_conntrack_timeout.h | 2 +-
include/net/netfilter/nf_tables.h | 6 +++---
include/uapi/linux/netfilter_bridge/ebt_among.h | 2 +-
net/bridge/netfilter/ebtables.c | 2 +-
net/ipv4/netfilter/arp_tables.c | 4 ++--
net/ipv4/netfilter/ip_tables.c | 4 ++--
net/ipv6/netfilter/ip6_tables.c | 4 ++--
net/netfilter/ipset/ip_set_bitmap_ip.c | 2 +-
net/netfilter/ipset/ip_set_bitmap_ipmac.c | 2 +-
net/netfilter/ipset/ip_set_bitmap_port.c | 2 +-
net/netfilter/ipset/ip_set_hash_gen.h | 4 ++--
net/netfilter/nfnetlink_acct.c | 2 +-
net/netfilter/nft_set_pipapo.c | 2 +-
net/netfilter/xt_hashlimit.c | 2 +-
net/netfilter/xt_recent.c | 4 ++--
22 files changed, 32 insertions(+), 32 deletions(-)

diff --git a/include/linux/netfilter/ipset/ip_set.h b/include/linux/netfilter/ipset/ip_set.h
index 908d38dbcb91..155eca0ed68d 100644
--- a/include/linux/netfilter/ipset/ip_set.h
+++ b/include/linux/netfilter/ipset/ip_set.h
@@ -98,7 +98,7 @@ struct ip_set_counter {

struct ip_set_comment_rcu {
struct rcu_head rcu;
- char str[0];
+ char str[];
};

struct ip_set_comment {
diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 1b261c51b3a3..5da88451853b 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -264,7 +264,7 @@ struct xt_table_info {
unsigned int stacksize;
void ***jumpstack;

- unsigned char entries[0] __aligned(8);
+ unsigned char entries[] __aligned(8);
};

int xt_register_target(struct xt_target *target);
@@ -464,7 +464,7 @@ struct compat_xt_entry_match {
} kernel;
u_int16_t match_size;
} u;
- unsigned char data[0];
+ unsigned char data[];
};

struct compat_xt_entry_target {
@@ -480,7 +480,7 @@ struct compat_xt_entry_target {
} kernel;
u_int16_t target_size;
} u;
- unsigned char data[0];
+ unsigned char data[];
};

/* FIXME: this works only on 32 bit tasks
@@ -494,7 +494,7 @@ struct compat_xt_counters {
struct compat_xt_counters_info {
char name[XT_TABLE_MAXNAMELEN];
compat_uint_t num_counters;
- struct compat_xt_counters counters[0];
+ struct compat_xt_counters counters[];
};

struct _compat_xt_align {
diff --git a/include/linux/netfilter_arp/arp_tables.h b/include/linux/netfilter_arp/arp_tables.h
index e98028f00e47..7d3537c40ec9 100644
--- a/include/linux/netfilter_arp/arp_tables.h
+++ b/include/linux/netfilter_arp/arp_tables.h
@@ -67,7 +67,7 @@ struct compat_arpt_entry {
__u16 next_offset;
compat_uint_t comefrom;
struct compat_xt_counters counters;
- unsigned char elems[0];
+ unsigned char elems[];
};

static inline struct xt_entry_target *
diff --git a/include/linux/netfilter_bridge/ebtables.h b/include/linux/netfilter_bridge/ebtables.h
index 162f59d0d17a..2f5c4e6ecd8a 100644
--- a/include/linux/netfilter_bridge/ebtables.h
+++ b/include/linux/netfilter_bridge/ebtables.h
@@ -85,7 +85,7 @@ struct ebt_table_info {
/* room to maintain the stack used for jumping from and into udc */
struct ebt_chainstack **chainstack;
char *entries;
- struct ebt_counter counters[0] ____cacheline_aligned;
+ struct ebt_counter counters[] ____cacheline_aligned;
};

struct ebt_table {
diff --git a/include/linux/netfilter_ipv4/ip_tables.h b/include/linux/netfilter_ipv4/ip_tables.h
index e9e1ed74cdf1..b394bd4f68a3 100644
--- a/include/linux/netfilter_ipv4/ip_tables.h
+++ b/include/linux/netfilter_ipv4/ip_tables.h
@@ -76,7 +76,7 @@ struct compat_ipt_entry {
__u16 next_offset;
compat_uint_t comefrom;
struct compat_xt_counters counters;
- unsigned char elems[0];
+ unsigned char elems[];
};

/* Helper functions */
diff --git a/include/linux/netfilter_ipv6/ip6_tables.h b/include/linux/netfilter_ipv6/ip6_tables.h
index 78ab959c4575..8225f7821a29 100644
--- a/include/linux/netfilter_ipv6/ip6_tables.h
+++ b/include/linux/netfilter_ipv6/ip6_tables.h
@@ -43,7 +43,7 @@ struct compat_ip6t_entry {
__u16 next_offset;
compat_uint_t comefrom;
struct compat_xt_counters counters;
- unsigned char elems[0];
+ unsigned char elems[];
};

static inline struct xt_entry_target *
diff --git a/include/net/netfilter/nf_conntrack_extend.h b/include/net/netfilter/nf_conntrack_extend.h
index 5ae5295aa46d..e1e588387103 100644
--- a/include/net/netfilter/nf_conntrack_extend.h
+++ b/include/net/netfilter/nf_conntrack_extend.h
@@ -45,7 +45,7 @@ enum nf_ct_ext_id {
struct nf_ct_ext {
u8 offset[NF_CT_EXT_NUM];
u8 len;
- char data[0];
+ char data[];
};

static inline bool __nf_ct_ext_exist(const struct nf_ct_ext *ext, u8 id)
diff --git a/include/net/netfilter/nf_conntrack_timeout.h b/include/net/netfilter/nf_conntrack_timeout.h
index 6dd72396f534..659b0ea25b4d 100644
--- a/include/net/netfilter/nf_conntrack_timeout.h
+++ b/include/net/netfilter/nf_conntrack_timeout.h
@@ -14,7 +14,7 @@
struct nf_ct_timeout {
__u16 l3num;
const struct nf_conntrack_l4proto *l4proto;
- char data[0];
+ char data[];
};

struct ctnl_timeout {
diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 4170c033d461..abcb4c89b0f9 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -224,7 +224,7 @@ int nft_validate_register_store(const struct nft_ctx *ctx,
*/
struct nft_userdata {
u8 len;
- unsigned char data[0];
+ unsigned char data[];
};

/**
@@ -572,7 +572,7 @@ struct nft_set_ext_tmpl {
struct nft_set_ext {
u8 genmask;
u8 offset[NFT_SET_EXT_NUM];
- char data[0];
+ char data[];
};

static inline void nft_set_ext_prepare(struct nft_set_ext_tmpl *tmpl)
@@ -1385,7 +1385,7 @@ struct nft_trans {
int msg_type;
bool put_net;
struct nft_ctx ctx;
- char data[0];
+ char data[];
};

struct nft_trans_rule {
diff --git a/include/uapi/linux/netfilter_bridge/ebt_among.h b/include/uapi/linux/netfilter_bridge/ebt_among.h
index 9acf757bc1f7..73b26a280c4f 100644
--- a/include/uapi/linux/netfilter_bridge/ebt_among.h
+++ b/include/uapi/linux/netfilter_bridge/ebt_among.h
@@ -40,7 +40,7 @@ struct ebt_mac_wormhash_tuple {
struct ebt_mac_wormhash {
int table[257];
int poolsize;
- struct ebt_mac_wormhash_tuple pool[0];
+ struct ebt_mac_wormhash_tuple pool[];
};

#define ebt_mac_wormhash_size(x) ((x) ? sizeof(struct ebt_mac_wormhash) \
diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index e1256e03a9a8..78db58c7aec2 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1561,7 +1561,7 @@ 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 f1f78a742b36..b167f4a5b684 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)
@@ -1383,7 +1383,7 @@ 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 10b91ebdf213..c2670eaa74e6 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
@@ -1562,7 +1562,7 @@ 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 c973ace208c5..e27393498ecb 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -1227,7 +1227,7 @@ 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
@@ -1571,7 +1571,7 @@ 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 0a2196f59106..486959f70cf3 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 739e343efaf6..2310a316e0af 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 b49978dd810d..e56ced66f202 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 7480ce55b5c8..f1edc5b9b4ce 100644
--- a/net/netfilter/ipset/ip_set_hash_gen.h
+++ b/net/netfilter/ipset/ip_set_hash_gen.h
@@ -68,7 +68,7 @@ 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));
};

@@ -77,7 +77,7 @@ struct htable {
atomic_t ref; /* References for resizing */
atomic_t uref; /* References for dumping */
u8 htable_bits; /* size of hash table == 2^htable_bits */
- 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 2481470dec36..5827117f2635 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/nft_set_pipapo.c b/net/netfilter/nft_set_pipapo.c
index feac8553f6d9..141cea0c5da2 100644
--- a/net/netfilter/nft_set_pipapo.c
+++ b/net/netfilter/nft_set_pipapo.c
@@ -433,7 +433,7 @@ struct nft_pipapo_match {
unsigned long * __percpu *scratch;
size_t bsize_max;
struct rcu_head rcu;
- struct nft_pipapo_field f[0];
+ struct nft_pipapo_field f[];
};

/* Current working bitmap index, toggled between field matches */
diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 7a2c4b8408c4..c687509d882e 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 0a9708004e20..6e6bc5b91199 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 {
--
2.25.0

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