[PATCH net-next 2/2] ipv4: igmp: convert ip_mc_msfget() to sockopt_t

[Breno Leitao <leitao@debian.org>]

IP_MSFILTER reads its reply through ip_mc_msfget(), reached from
do_ip_getsockopt() and from nowhere else. Convert it, and build the
sockopt_t at the call site for as long as the caller still carries a
sockptr_t pair.

This is a special case, where optlen might only point
to the header, and the real structure size is inside the header.

This is nasty, but, in order to avoid breaking userspace, we need to
preserve the same mechanism, by:

1) Only applying it for userspace address, otherwise it is too risky
2) Assume there is room to support the new size (in userspace)

The source list also moves from copy_to_sockptr_offset() to a sequential
copy_to_iter(). IP_MSFILTER_SIZE(0) and offsetof(struct ip_msfilter,
imsf_slist_flex) are both 16, so the bytes land where they did.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/linux/igmp.h   |  3 ++-
 net/ipv4/igmp.c        | 23 ++++++++++++++---------
 net/ipv4/ip_sockglue.c | 10 +++++++++-
 3 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/include/linux/igmp.h b/include/linux/igmp.h
index a0cf0398519fd7..e075611344ef3b 100644
--- a/include/linux/igmp.h
+++ b/include/linux/igmp.h
@@ -14,6 +14,7 @@
 #include <linux/timer.h>
 #include <linux/in.h>
 #include <linux/ip.h>
+#include <linux/net.h>
 #include <linux/refcount.h>
 #include <linux/sockptr.h>
 #include <uapi/linux/igmp.h>
@@ -273,7 +274,7 @@ extern int ip_mc_source(int add, int omode, struct sock *sk,
 		struct ip_mreq_source *mreqs, int ifindex);
 extern int ip_mc_msfilter(struct sock *sk, struct ip_msfilter *msf,int ifindex);
 extern int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
-			sockptr_t optval, sockptr_t optlen);
+			sockopt_t *opt);
 extern int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
 			sockptr_t optval, size_t offset);
 extern int ip_mc_sf_allow(const struct sock *sk, __be32 local, __be32 rmt,
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index d56355aca79776..144fca158adcb0 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -2709,8 +2709,8 @@ int ip_mc_msfilter(struct sock *sk, struct ip_msfilter *msf, int ifindex)
 		err = ip_mc_leave_group(sk, &imr);
 	return err;
 }
-int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
-		 sockptr_t optval, sockptr_t optlen)
+
+int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf, sockopt_t *opt)
 {
 	int err, len, count, copycount, msf_size;
 	struct ip_mreqn	imr;
@@ -2755,14 +2755,19 @@ int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
 	len = flex_array_size(psl, sl_addr, copycount);
 	msf->imsf_numsrc = count;
 	msf_size = IP_MSFILTER_SIZE(copycount);
-	if (copy_to_sockptr(optlen, &msf_size, sizeof(int)) ||
-	    copy_to_sockptr(optval, msf, IP_MSFILTER_SIZE(0))) {
+
+	/* The source list is sized by the imsf_numsrc the caller left in
+	 * optval, not by optlen, which only has to cover the fixed part.
+	 */
+	err = sockopt_expand_out(opt, msf_size);
+	if (err)
+		return err;
+
+	opt->optlen = msf_size;
+	if (copy_to_iter(msf, IP_MSFILTER_SIZE(0), &opt->iter_out) !=
+	    IP_MSFILTER_SIZE(0))
 		return -EFAULT;
-	}
-	if (len &&
-	    copy_to_sockptr_offset(optval,
-				   offsetof(struct ip_msfilter, imsf_slist_flex),
-				   psl->sl_addr, len))
+	if (len && copy_to_iter(psl->sl_addr, len, &opt->iter_out) != len)
 		return -EFAULT;
 	return 0;
 done:
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index a55ef327ec932c..c58e565f2a5aa7 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1706,6 +1706,8 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 	case IP_MSFILTER:
 	{
 		struct ip_msfilter msf;
+		struct kvec kvec;
+		sockopt_t opt;
 
 		if (len < IP_MSFILTER_SIZE(0)) {
 			err = -EINVAL;
@@ -1715,7 +1717,13 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 			err = -EFAULT;
 			goto out;
 		}
-		err = ip_mc_msfget(sk, &msf, optval, optlen);
+		err = sockptr_to_sockopt(&opt, optval, optlen, &kvec);
+		if (err)
+			goto out;
+
+		err = ip_mc_msfget(sk, &msf, &opt);
+		if (copy_to_sockptr(optlen, &opt.optlen, sizeof(int)))
+			err = -EFAULT;
 		goto out;
 	}
 	case MCAST_MSFILTER:

-- 
2.53.0-Meta