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

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[ 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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>
Stable-dep-of: 542ed8145e6f ("netfilter: nft_set_hash: unaligned atomic read on struct nft_set_ext")
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Gustavo A. R. Silva 2020-02-20 07:59:14 -06:00 • committed by Greg Kroah-Hartman
commit 9857e028d4
21 changed files with 31 additions and 31 deletions
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4
net/ipv4/netfilter/arp_tables.c
View file

@ -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,

4
net/ipv4/netfilter/ip_tables.c
View file

@ -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