[PATCH v3 4/6] linux-user: netlink: Add emulation of IP_MULTICAST_IF

[deller@kernel.org]

From: Helge Deller <deller@gmx.de>

Add IP_MULTICAST_IF and share the code with IP_ADD_MEMBERSHIP / IP_DROP_MEMBERSHIP.
Sharing the code makes sense, because the manpage of ip(7)  says:

IP_MULTICAST_IF (since Linux 1.2)
      Set the local device for a multicast socket.  The argument
      for setsockopt(2) is an ip_mreqn or (since Linux 3.5)
      ip_mreq structure similar to IP_ADD_MEMBERSHIP, or an
      in_addr structure.  (The kernel determines which structure
      is being passed based on the size passed in optlen.)  For
      getsockopt(2), the argument is an in_addr structure.

Signed-off-by: Helge Deller <deller@gmx.de>

v2: (based on feedback by Laurent Vivier)
- refined commit message and restructure the copying of ip_mreqn fields

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index bbe2560927..4360543e20 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -2130,16 +2130,23 @@ static abi_long do_setsockopt(int sockfd, int level, int optname,
             }
             ret = get_errno(setsockopt(sockfd, level, optname, &val, sizeof(val)));
             break;
+        case IP_MULTICAST_IF:
         case IP_ADD_MEMBERSHIP:
         case IP_DROP_MEMBERSHIP:
         {
             struct ip_mreqn ip_mreq;
             struct target_ip_mreqn *target_smreqn;
+            int min_size;

             QEMU_BUILD_BUG_ON(sizeof(struct ip_mreq) !=
                               sizeof(struct target_ip_mreq));

-            if (optlen < sizeof (struct target_ip_mreq) ||
+            if (optname == IP_MULTICAST_IF) {
+                min_size = sizeof(struct in_addr);
+            } else {
+                min_size = sizeof(struct target_ip_mreq);
+            }
+            if (optlen < min_size ||
                 optlen > sizeof (struct target_ip_mreqn)) {
                 return -TARGET_EINVAL;
             }
@@ -2149,7 +2156,9 @@ static abi_long do_setsockopt(int sockfd, int level, int optname,
                 return -TARGET_EFAULT;
             }
             ip_mreq.imr_multiaddr.s_addr = target_smreqn->imr_multiaddr.s_addr;
-            ip_mreq.imr_address.s_addr = target_smreqn->imr_address.s_addr;
+            if (optlen >= sizeof(struct target_ip_mreq)) {
+                ip_mreq.imr_address.s_addr = target_smreqn->imr_address.s_addr;
+            }
             if (optlen == sizeof(struct target_ip_mreqn)) {
                 ip_mreq.imr_ifindex = tswapal(target_smreqn->imr_ifindex);
                 optlen = sizeof(struct ip_mreqn);
---
 linux-user/syscall.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index df8609b4d8..6ee02383da 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -2130,16 +2130,23 @@ static abi_long do_setsockopt(int sockfd, int level, int optname,
             }
             ret = get_errno(setsockopt(sockfd, level, optname, &val, sizeof(val)));
             break;
+        case IP_MULTICAST_IF:
         case IP_ADD_MEMBERSHIP:
         case IP_DROP_MEMBERSHIP:
         {
             struct ip_mreqn ip_mreq;
             struct target_ip_mreqn *target_smreqn;
+            int min_size;
 
             QEMU_BUILD_BUG_ON(sizeof(struct ip_mreq) !=
                               sizeof(struct target_ip_mreq));
 
-            if (optlen < sizeof (struct target_ip_mreq) ||
+            if (optname == IP_MULTICAST_IF) {
+                min_size = sizeof(struct in_addr);
+            } else {
+                min_size = sizeof(struct target_ip_mreq);
+            }
+            if (optlen < min_size ||
                 optlen > sizeof (struct target_ip_mreqn)) {
                 return -TARGET_EINVAL;
             }
@@ -2149,13 +2156,14 @@ static abi_long do_setsockopt(int sockfd, int level, int optname,
                 return -TARGET_EFAULT;
             }
             ip_mreq.imr_multiaddr.s_addr = target_smreqn->imr_multiaddr.s_addr;
-            ip_mreq.imr_address.s_addr = target_smreqn->imr_address.s_addr;
-            if (optlen == sizeof(struct target_ip_mreqn)) {
-                ip_mreq.imr_ifindex = tswapal(target_smreqn->imr_ifindex);
-                optlen = sizeof(struct ip_mreqn);
+            if (optlen >= sizeof(struct target_ip_mreq)) {
+                ip_mreq.imr_address.s_addr = target_smreqn->imr_address.s_addr;
+                if (optlen >= sizeof(struct target_ip_mreqn)) {
+                    __put_user(target_smreqn->imr_ifindex, &ip_mreq.imr_ifindex);
+                    optlen = sizeof(struct ip_mreqn);
+                }
             }
             unlock_user(target_smreqn, optval_addr, 0);
-
             ret = get_errno(setsockopt(sockfd, level, optname, &ip_mreq, optlen));
             break;
         }
-- 
2.47.0