linux-user: fix recvmsg()/recvfrom() with netlink and MSG_TRUNC

If recvmsg()/recvfrom() are used with the MSG_TRUNC flag, they return the
real length even if it was longer than the passed buffer.
So when we translate the buffer we must check we don't go beyond the
end of the buffer.

Bug: https://github.com/vivier/qemu-m68k/issues/33
Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20180820171557.7734-2-laurent@vivier.eu>

1 files changed, 7 insertions, 2 deletions

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 1806b33b02..e66faf1c62 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -3892,7 +3892,7 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
             len = ret;
             if (fd_trans_host_to_target_data(fd)) {
                 ret = fd_trans_host_to_target_data(fd)(msg.msg_iov->iov_base,
-                                                       len);
+                                               MIN(msg.msg_iov->iov_len, len));
             } else {
                 ret = host_to_target_cmsg(msgp, &msg);
             }
@@ -4169,7 +4169,12 @@ static abi_long do_recvfrom(int fd, abi_ulong msg, size_t len, int flags,
     }
     if (!is_error(ret)) {
         if (fd_trans_host_to_target_data(fd)) {
-            ret = fd_trans_host_to_target_data(fd)(host_msg, ret);
+            abi_long trans;
+            trans = fd_trans_host_to_target_data(fd)(host_msg, MIN(ret, len));
+            if (is_error(trans)) {
+                ret = trans;
+                goto fail;
+            }
         }
         if (target_addr) {
             host_to_target_sockaddr(target_addr, addr, addrlen);