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>

diff --git a/include/net/compat.h b/include/net/compat.h
index 84805bd..595fee0 100644 (file)
--- a/include/net/compat.h
+++ b/include/net/compat.h
@@ -71,13 +71,26 @@ struct compat_group_source_req {
 } __packed;
 
 struct compat_group_filter {
-       __u32                            gf_interface;
-       struct __kernel_sockaddr_storage gf_group
-               __aligned(4);
-       __u32                            gf_fmode;
-       __u32                            gf_numsrc;
-       struct __kernel_sockaddr_storage gf_slist[1]
-               __aligned(4);
+       union {
+               struct {
+                       __u32                            gf_interface_aux;
+                       struct __kernel_sockaddr_storage gf_group_aux
+                               __aligned(4);
+                       __u32                            gf_fmode_aux;
+                       __u32                            gf_numsrc_aux;
+                       struct __kernel_sockaddr_storage gf_slist[1]
+                               __aligned(4);
+               } __packed;
+               struct {
+                       __u32                            gf_interface;
+                       struct __kernel_sockaddr_storage gf_group
+                               __aligned(4);
+                       __u32                            gf_fmode;
+                       __u32                            gf_numsrc;
+                       struct __kernel_sockaddr_storage gf_slist_flex[]
+                               __aligned(4);
+               } __packed;
+       };
 } __packed;
 
 #endif /* NET_COMPAT_H */

diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
index 193b7cf..1416822 100644 (file)
--- 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) \

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 468969c..b297bb2 100644 (file)
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -790,7 +790,8 @@ static int ip_set_mcast_msfilter(struct sock *sk, sockptr_t optval, int optlen)
                goto out_free_gsf;
 
        err = set_mcast_msfilter(sk, gsf->gf_interface, gsf->gf_numsrc,
-                                gsf->gf_fmode, &gsf->gf_group, gsf->gf_slist);
+                                gsf->gf_fmode, &gsf->gf_group,
+                                gsf->gf_slist_flex);
 out_free_gsf:
        kfree(gsf);
        return err;
@@ -799,7 +800,7 @@ out_free_gsf:
 static int compat_ip_set_mcast_msfilter(struct sock *sk, sockptr_t optval,
                int optlen)
 {
-       const int size0 = offsetof(struct compat_group_filter, gf_slist);
+       const int size0 = offsetof(struct compat_group_filter, gf_slist_flex);
        struct compat_group_filter *gf32;
        unsigned int n;
        void *p;
@@ -813,7 +814,7 @@ static int compat_ip_set_mcast_msfilter(struct sock *sk, sockptr_t optval,
        p = kmalloc(optlen + 4, GFP_KERNEL);
        if (!p)
                return -ENOMEM;
-       gf32 = p + 4; /* we want ->gf_group and ->gf_slist aligned */
+       gf32 = p + 4; /* we want ->gf_group and ->gf_slist_flex aligned */
 
        err = -EFAULT;
        if (copy_from_sockptr(gf32, optval, optlen))
@@ -826,7 +827,7 @@ static int compat_ip_set_mcast_msfilter(struct sock *sk, sockptr_t optval,
                goto out_free_gsf;
 
        err = -EINVAL;
-       if (offsetof(struct compat_group_filter, gf_slist[n]) > optlen)
+       if (offsetof(struct compat_group_filter, gf_slist_flex[n]) > optlen)
                goto out_free_gsf;
 
        /* numsrc >= (4G-140)/128 overflow in 32 bits */
@@ -834,7 +835,7 @@ static int compat_ip_set_mcast_msfilter(struct sock *sk, sockptr_t optval,
        if (n > sock_net(sk)->ipv4.sysctl_igmp_max_msf)
                goto out_free_gsf;
        err = set_mcast_msfilter(sk, gf32->gf_interface, n, gf32->gf_fmode,
-                                &gf32->gf_group, gf32->gf_slist);
+                                &gf32->gf_group, gf32->gf_slist_flex);
 out_free_gsf:
        kfree(p);
        return err;
@@ -1455,7 +1456,7 @@ static bool getsockopt_needs_rtnl(int optname)
 static int ip_get_mcast_msfilter(struct sock *sk, void __user *optval,
                int __user *optlen, int len)
 {
-       const int size0 = offsetof(struct group_filter, gf_slist);
+       const int size0 = offsetof(struct group_filter, gf_slist_flex);
        struct group_filter __user *p = optval;
        struct group_filter gsf;
        int num;
@@ -1467,7 +1468,7 @@ static int ip_get_mcast_msfilter(struct sock *sk, void __user *optval,
                return -EFAULT;
 
        num = gsf.gf_numsrc;
-       err = ip_mc_gsfget(sk, &gsf, p->gf_slist);
+       err = ip_mc_gsfget(sk, &gsf, p->gf_slist_flex);
        if (err)
                return err;
        if (gsf.gf_numsrc < num)
@@ -1481,7 +1482,7 @@ static int ip_get_mcast_msfilter(struct sock *sk, void __user *optval,
 static int compat_ip_get_mcast_msfilter(struct sock *sk, void __user *optval,
                int __user *optlen, int len)
 {
-       const int size0 = offsetof(struct compat_group_filter, gf_slist);
+       const int size0 = offsetof(struct compat_group_filter, gf_slist_flex);
        struct compat_group_filter __user *p = optval;
        struct compat_group_filter gf32;
        struct group_filter gf;
@@ -1498,7 +1499,7 @@ static int compat_ip_get_mcast_msfilter(struct sock *sk, void __user *optval,
        num = gf.gf_numsrc = gf32.gf_numsrc;
        gf.gf_group = gf32.gf_group;
 
-       err = ip_mc_gsfget(sk, &gf, p->gf_slist);
+       err = ip_mc_gsfget(sk, &gf, p->gf_slist_flex);
        if (err)
                return err;
        if (gf.gf_numsrc < num)

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index a6804a7..e4bdb09 100644 (file)
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -225,7 +225,7 @@ static int ipv6_set_mcast_msfilter(struct sock *sk, sockptr_t optval,
        if (GROUP_FILTER_SIZE(gsf->gf_numsrc) > optlen)
                goto out_free_gsf;
 
-       ret = ip6_mc_msfilter(sk, gsf, gsf->gf_slist);
+       ret = ip6_mc_msfilter(sk, gsf, gsf->gf_slist_flex);
 out_free_gsf:
        kfree(gsf);
        return ret;
@@ -234,7 +234,7 @@ out_free_gsf:
 static int compat_ipv6_set_mcast_msfilter(struct sock *sk, sockptr_t optval,
                int optlen)
 {
-       const int size0 = offsetof(struct compat_group_filter, gf_slist);
+       const int size0 = offsetof(struct compat_group_filter, gf_slist_flex);
        struct compat_group_filter *gf32;
        void *p;
        int ret;
@@ -249,7 +249,7 @@ static int compat_ipv6_set_mcast_msfilter(struct sock *sk, sockptr_t optval,
        if (!p)
                return -ENOMEM;
 
-       gf32 = p + 4; /* we want ->gf_group and ->gf_slist aligned */
+       gf32 = p + 4; /* we want ->gf_group and ->gf_slist_flex aligned */
        ret = -EFAULT;
        if (copy_from_sockptr(gf32, optval, optlen))
                goto out_free_p;
@@ -261,14 +261,14 @@ static int compat_ipv6_set_mcast_msfilter(struct sock *sk, sockptr_t optval,
                goto out_free_p;
 
        ret = -EINVAL;
-       if (offsetof(struct compat_group_filter, gf_slist[n]) > optlen)
+       if (offsetof(struct compat_group_filter, gf_slist_flex[n]) > optlen)
                goto out_free_p;
 
        ret = ip6_mc_msfilter(sk, &(struct group_filter){
                        .gf_interface = gf32->gf_interface,
                        .gf_group = gf32->gf_group,
                        .gf_fmode = gf32->gf_fmode,
-                       .gf_numsrc = gf32->gf_numsrc}, gf32->gf_slist);
+                       .gf_numsrc = gf32->gf_numsrc}, gf32->gf_slist_flex);
 
 out_free_p:
        kfree(p);
@@ -1048,7 +1048,7 @@ static int ipv6_getsockopt_sticky(struct sock *sk, struct ipv6_txoptions *opt,
 static int ipv6_get_msfilter(struct sock *sk, void __user *optval,
                int __user *optlen, int len)
 {
-       const int size0 = offsetof(struct group_filter, gf_slist);
+       const int size0 = offsetof(struct group_filter, gf_slist_flex);
        struct group_filter __user *p = optval;
        struct group_filter gsf;
        int num;
@@ -1062,7 +1062,7 @@ static int ipv6_get_msfilter(struct sock *sk, void __user *optval,
                return -EADDRNOTAVAIL;
        num = gsf.gf_numsrc;
        lock_sock(sk);
-       err = ip6_mc_msfget(sk, &gsf, p->gf_slist);
+       err = ip6_mc_msfget(sk, &gsf, p->gf_slist_flex);
        if (!err) {
                if (num > gsf.gf_numsrc)
                        num = gsf.gf_numsrc;
@@ -1077,7 +1077,7 @@ static int ipv6_get_msfilter(struct sock *sk, void __user *optval,
 static int compat_ipv6_get_msfilter(struct sock *sk, void __user *optval,
                int __user *optlen)
 {
-       const int size0 = offsetof(struct compat_group_filter, gf_slist);
+       const int size0 = offsetof(struct compat_group_filter, gf_slist_flex);
        struct compat_group_filter __user *p = optval;
        struct compat_group_filter gf32;
        struct group_filter gf;
@@ -1100,7 +1100,7 @@ static int compat_ipv6_get_msfilter(struct sock *sk, void __user *optval,
                return -EADDRNOTAVAIL;
 
        lock_sock(sk);
-       err = ip6_mc_msfget(sk, &gf, p->gf_slist);
+       err = ip6_mc_msfget(sk, &gf, p->gf_slist_flex);
        release_sock(sk);
        if (err)
                return err;