linux-user: Fix accept4(SOCK_NONBLOCK) syscall

The Linux accept4() syscall allows two flags only: SOCK_NONBLOCK and
SOCK_CLOEXEC, and returns -EINVAL if any other bits have been set.

Change the qemu implementation accordingly, which means we can not use
the fcntl_flags_tbl[] translation table which allows too many other
values.

Beside the correction in behaviour, this actually fixes the accept4()
emulation for hppa, mips and alpha targets for which SOCK_NONBLOCK is
different than TARGET_SOCK_NONBLOCK (aka O_NONBLOCK).

The fix can be verified with the testcase of the debian lwt package,
which hangs forever in a read() syscall without this patch.

Signed-off-by: Helge Deller <deller@gmx.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit dca4c83)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

linux-user/syscall.c

@@ -3440,7 +3440,17 @@ static abi_long do_accept4(int fd, abi_ulong target_addr,
     abi_long ret;
     int host_flags;
 
-    host_flags = target_to_host_bitmask(flags, fcntl_flags_tbl);
+    if (flags & ~(TARGET_SOCK_CLOEXEC | TARGET_SOCK_NONBLOCK)) {
+        return -TARGET_EINVAL;
+    }
+
+    host_flags = 0;
+    if (flags & TARGET_SOCK_NONBLOCK) {
+        host_flags |= SOCK_NONBLOCK;
+    }
+    if (flags & TARGET_SOCK_CLOEXEC) {
+        host_flags |= SOCK_CLOEXEC;
+    }
 
     if (target_addr == 0) {
         return get_errno(safe_accept4(fd, NULL, NULL, host_flags));