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| author | Gustavo A. R. Silva <gustavoars@kernel.org> | 2021-08-04 15:45:36 -0500 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2021-08-05 11:46:42 +0100 |
| commit | db243b796439c0caba47865564d8acd18a301d18 (patch) | |
| tree | 4d9286e7e1146337ff111a5cf0b2552dc9cc5195 /include/uapi/linux/in.h | |
| parent | d15040a33883c3ab2ee2ea17e6427ce24e9f3ac0 (diff) | |
| download | lwn-db243b796439c0caba47865564d8acd18a301d18.tar.gz lwn-db243b796439c0caba47865564d8acd18a301d18.zip | |
net/ipv4/ipv6: Replace one-element arraya with flexible-array members
There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].
Use an anonymous union with a couple of anonymous structs in order to
keep userspace unchanged and refactor the related code accordingly:
$ pahole -C group_filter net/ipv4/ip_sockglue.o
struct group_filter {
union {
struct {
__u32 gf_interface_aux; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
struct __kernel_sockaddr_storage gf_group_aux; /* 8 128 */
/* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */
__u32 gf_fmode_aux; /* 136 4 */
__u32 gf_numsrc_aux; /* 140 4 */
struct __kernel_sockaddr_storage gf_slist[1]; /* 144 128 */
}; /* 0 272 */
struct {
__u32 gf_interface; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
struct __kernel_sockaddr_storage gf_group; /* 8 128 */
/* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */
__u32 gf_fmode; /* 136 4 */
__u32 gf_numsrc; /* 140 4 */
struct __kernel_sockaddr_storage gf_slist_flex[0]; /* 144 0 */
}; /* 0 144 */
}; /* 0 272 */
/* size: 272, cachelines: 5, members: 1 */
/* last cacheline: 16 bytes */
};
$ pahole -C compat_group_filter net/ipv4/ip_sockglue.o
struct compat_group_filter {
union {
struct {
__u32 gf_interface_aux; /* 0 4 */
struct __kernel_sockaddr_storage gf_group_aux __attribute__((__aligned__(4))); /* 4 128 */
/* --- cacheline 2 boundary (128 bytes) was 4 bytes ago --- */
__u32 gf_fmode_aux; /* 132 4 */
__u32 gf_numsrc_aux; /* 136 4 */
struct __kernel_sockaddr_storage gf_slist[1] __attribute__((__aligned__(4))); /* 140 128 */
} __attribute__((__packed__)) __attribute__((__aligned__(4))); /* 0 268 */
struct {
__u32 gf_interface; /* 0 4 */
struct __kernel_sockaddr_storage gf_group __attribute__((__aligned__(4))); /* 4 128 */
/* --- cacheline 2 boundary (128 bytes) was 4 bytes ago --- */
__u32 gf_fmode; /* 132 4 */
__u32 gf_numsrc; /* 136 4 */
struct __kernel_sockaddr_storage gf_slist_flex[0] __attribute__((__aligned__(4))); /* 140 0 */
} __attribute__((__packed__)) __attribute__((__aligned__(4))); /* 0 140 */
} __attribute__((__aligned__(1))); /* 0 268 */
/* size: 268, cachelines: 5, members: 1 */
/* forced alignments: 1 */
/* last cacheline: 12 bytes */
} __attribute__((__packed__));
This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().
[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/uapi/linux/in.h')
| -rw-r--r-- | include/uapi/linux/in.h | 21 |
1 files changed, 16 insertions, 5 deletions
diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h index 193b7cf1f0ac..14168225cecd 100644 --- a/include/uapi/linux/in.h +++ b/include/uapi/linux/in.h @@ -222,11 +222,22 @@ struct group_source_req { }; struct group_filter { - __u32 gf_interface; /* interface index */ - struct __kernel_sockaddr_storage gf_group; /* multicast address */ - __u32 gf_fmode; /* filter mode */ - __u32 gf_numsrc; /* number of sources */ - struct __kernel_sockaddr_storage gf_slist[1]; /* interface index */ + union { + struct { + __u32 gf_interface_aux; /* interface index */ + struct __kernel_sockaddr_storage gf_group_aux; /* multicast address */ + __u32 gf_fmode_aux; /* filter mode */ + __u32 gf_numsrc_aux; /* number of sources */ + struct __kernel_sockaddr_storage gf_slist[1]; /* interface index */ + }; + struct { + __u32 gf_interface; /* interface index */ + struct __kernel_sockaddr_storage gf_group; /* multicast address */ + __u32 gf_fmode; /* filter mode */ + __u32 gf_numsrc; /* number of sources */ + struct __kernel_sockaddr_storage gf_slist_flex[]; /* interface index */ + }; + }; }; #define GROUP_FILTER_SIZE(numsrc) \ |