linux/include/net/mld.h
Gustavo A. R. Silva c61a2a76e5 net: ipv6: mld: Replace zero-length array with flexible-array member
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]

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 <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2020-02-29 21:52:20 -08:00

115 lines
2.8 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef LINUX_MLD_H
#define LINUX_MLD_H
#include <linux/in6.h>
#include <linux/icmpv6.h>
/* MLDv1 Query/Report/Done */
struct mld_msg {
struct icmp6hdr mld_hdr;
struct in6_addr mld_mca;
};
#define mld_type mld_hdr.icmp6_type
#define mld_code mld_hdr.icmp6_code
#define mld_cksum mld_hdr.icmp6_cksum
#define mld_maxdelay mld_hdr.icmp6_maxdelay
#define mld_reserved mld_hdr.icmp6_dataun.un_data16[1]
/* Multicast Listener Discovery version 2 headers */
/* MLDv2 Report */
struct mld2_grec {
__u8 grec_type;
__u8 grec_auxwords;
__be16 grec_nsrcs;
struct in6_addr grec_mca;
struct in6_addr grec_src[];
};
struct mld2_report {
struct icmp6hdr mld2r_hdr;
struct mld2_grec mld2r_grec[];
};
#define mld2r_type mld2r_hdr.icmp6_type
#define mld2r_resv1 mld2r_hdr.icmp6_code
#define mld2r_cksum mld2r_hdr.icmp6_cksum
#define mld2r_resv2 mld2r_hdr.icmp6_dataun.un_data16[0]
#define mld2r_ngrec mld2r_hdr.icmp6_dataun.un_data16[1]
/* MLDv2 Query */
struct mld2_query {
struct icmp6hdr mld2q_hdr;
struct in6_addr mld2q_mca;
#if defined(__LITTLE_ENDIAN_BITFIELD)
__u8 mld2q_qrv:3,
mld2q_suppress:1,
mld2q_resv2:4;
#elif defined(__BIG_ENDIAN_BITFIELD)
__u8 mld2q_resv2:4,
mld2q_suppress:1,
mld2q_qrv:3;
#else
#error "Please fix <asm/byteorder.h>"
#endif
__u8 mld2q_qqic;
__be16 mld2q_nsrcs;
struct in6_addr mld2q_srcs[];
};
#define mld2q_type mld2q_hdr.icmp6_type
#define mld2q_code mld2q_hdr.icmp6_code
#define mld2q_cksum mld2q_hdr.icmp6_cksum
#define mld2q_mrc mld2q_hdr.icmp6_maxdelay
#define mld2q_resv1 mld2q_hdr.icmp6_dataun.un_data16[1]
/* RFC3810, 5.1.3. Maximum Response Code:
*
* If Maximum Response Code >= 32768, Maximum Response Code represents a
* floating-point value as follows:
*
* 0 1 2 3 4 5 6 7 8 9 A B C D E F
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* |1| exp | mant |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
#define MLDV2_MRC_EXP(value) (((value) >> 12) & 0x0007)
#define MLDV2_MRC_MAN(value) ((value) & 0x0fff)
/* RFC3810, 5.1.9. QQIC (Querier's Query Interval Code):
*
* If QQIC >= 128, QQIC represents a floating-point value as follows:
*
* 0 1 2 3 4 5 6 7
* +-+-+-+-+-+-+-+-+
* |1| exp | mant |
* +-+-+-+-+-+-+-+-+
*/
#define MLDV2_QQIC_EXP(value) (((value) >> 4) & 0x07)
#define MLDV2_QQIC_MAN(value) ((value) & 0x0f)
#define MLD_EXP_MIN_LIMIT 32768UL
#define MLDV1_MRD_MAX_COMPAT (MLD_EXP_MIN_LIMIT - 1)
static inline unsigned long mldv2_mrc(const struct mld2_query *mlh2)
{
/* RFC3810, 5.1.3. Maximum Response Code */
unsigned long ret, mc_mrc = ntohs(mlh2->mld2q_mrc);
if (mc_mrc < MLD_EXP_MIN_LIMIT) {
ret = mc_mrc;
} else {
unsigned long mc_man, mc_exp;
mc_exp = MLDV2_MRC_EXP(mc_mrc);
mc_man = MLDV2_MRC_MAN(mc_mrc);
ret = (mc_man | 0x1000) << (mc_exp + 3);
}
return ret;
}
#endif