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net/ipv4: Replace one-element array with flexible-array member

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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:

$ pahole -C ip_msfilter net/ipv4/ip_sockglue.o
struct ip_msfilter {
	union {
		struct {
			__be32     imsf_multiaddr_aux;   /*     0     4 */
			__be32     imsf_interface_aux;   /*     4     4 */
			__u32      imsf_fmode_aux;       /*     8     4 */
			__u32      imsf_numsrc_aux;      /*    12     4 */
			__be32     imsf_slist[1];        /*    16     4 */
		};                                       /*     0    20 */
		struct {
			__be32     imsf_multiaddr;       /*     0     4 */
			__be32     imsf_interface;       /*     4     4 */
			__u32      imsf_fmode;           /*     8     4 */
			__u32      imsf_numsrc;          /*    12     4 */
			__be32     imsf_slist_flex[0];   /*    16     0 */
		};                                       /*     0    16 */
	};                                               /*     0    20 */

	/* size: 20, cachelines: 1, members: 1 */
	/* last cacheline: 20 bytes */
};

Also, refactor the code accordingly and make use of the struct_size()
and flex_array_size() helpers.

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>
This commit is contained in:
Gustavo A. R. Silva 2021-07-31 12:08:30 -05:00 committed by David S. Miller
parent 29a097b774
commit 2d3e5caf96
3 changed files with 30 additions and 18 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

13
include/uapi/linux/in.h
View file

@ -188,11 +188,22 @@ struct ip_mreq_source {
};
struct ip_msfilter {
union {
struct {
__be32 imsf_multiaddr_aux;
__be32 imsf_interface_aux;
__u32 imsf_fmode_aux;
__u32 imsf_numsrc_aux;
__be32 imsf_slist[1];
};
struct {
__be32 imsf_multiaddr;
__be32 imsf_interface;
__u32 imsf_fmode;
__u32 imsf_numsrc;
__be32 imsf_slist[1];
__be32 imsf_slist_flex[];
};
};
};
#define IP_MSFILTER_SIZE(numsrc) \

12
net/ipv4/igmp.c
View file

@ -2475,8 +2475,8 @@ int ip_mc_msfilter(struct sock *sk, struct ip_msfilter *msf, int ifindex)
goto done;
}
newpsl->sl_max = newpsl->sl_count = msf->imsf_numsrc;
memcpy(newpsl->sl_addr, msf->imsf_slist,
msf->imsf_numsrc * sizeof(msf->imsf_slist[0]));
memcpy(newpsl->sl_addr, msf->imsf_slist_flex,
flex_array_size(msf, imsf_slist_flex, msf->imsf_numsrc));
err = ip_mc_add_src(in_dev, &msf->imsf_multiaddr,
msf->imsf_fmode, newpsl->sl_count, newpsl->sl_addr, 0);
if (err) {
@ -2551,14 +2551,14 @@ int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
count = psl->sl_count;
}
copycount = count < msf->imsf_numsrc ? count : msf->imsf_numsrc;
len = copycount * sizeof(psl->sl_addr[0]);
len = flex_array_size(psl, sl_addr, copycount);
msf->imsf_numsrc = count;
if (put_user(IP_MSFILTER_SIZE(copycount), optlen) ||
copy_to_user(optval, msf, IP_MSFILTER_SIZE(0))) {
if (put_user(struct_size(optval, imsf_slist_flex, copycount), optlen) ||
copy_to_user(optval, msf, struct_size(optval, imsf_slist_flex, 0))) {
return -EFAULT;
}
if (len &&
copy_to_user(&optval->imsf_slist[0], psl->sl_addr, len))
copy_to_user(&optval->imsf_slist_flex[0], psl->sl_addr, len))
return -EFAULT;
return 0;
done:

15
net/ipv4/ip_sockglue.c
View file

@ -663,12 +663,11 @@ static int set_mcast_msfilter(struct sock *sk, int ifindex,
struct sockaddr_storage *group,
struct sockaddr_storage *list)
{
int msize = IP_MSFILTER_SIZE(numsrc);
struct ip_msfilter *msf;
struct sockaddr_in *psin;
int err, i;
msf = kmalloc(msize, GFP_KERNEL);
msf = kmalloc(struct_size(msf, imsf_slist_flex, numsrc), GFP_KERNEL);
if (!msf)
return -ENOBUFS;
@ -684,7 +683,7 @@ static int set_mcast_msfilter(struct sock *sk, int ifindex,
if (psin->sin_family != AF_INET)
goto Eaddrnotavail;
msf->imsf_slist[i] = psin->sin_addr.s_addr;
msf->imsf_slist_flex[i] = psin->sin_addr.s_addr;
}
err = ip_mc_msfilter(sk, msf, ifindex);
kfree(msf);
@ -1229,7 +1228,7 @@ static int do_ip_setsockopt(struct sock *sk, int level, int optname,
{
struct ip_msfilter *msf;
if (optlen < IP_MSFILTER_SIZE(0))
if (optlen < struct_size(msf, imsf_slist_flex, 0))
goto e_inval;
if (optlen > sysctl_optmem_max) {
err = -ENOBUFS;
@ -1247,7 +1246,8 @@ static int do_ip_setsockopt(struct sock *sk, int level, int optname,
err = -ENOBUFS;
break;
}
if (IP_MSFILTER_SIZE(msf->imsf_numsrc) > optlen) {
if (struct_size(msf, imsf_slist_flex, msf->imsf_numsrc) >
optlen) {
kfree(msf);
err = -EINVAL;
break;
@ -1660,11 +1660,12 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
{
struct ip_msfilter msf;
if (len < IP_MSFILTER_SIZE(0)) {
if (len < struct_size(&msf, imsf_slist_flex, 0)) {
err = -EINVAL;
goto out;
}
if (copy_from_user(&msf, optval, IP_MSFILTER_SIZE(0))) {
if (copy_from_user(&msf, optval,
struct_size(&msf, imsf_slist_flex, 0))) {
err = -EFAULT;
goto out;
}