[PATCH] hurd: Check return value of mach_port_mod_refs() in the dup routine of fcntl()

[Zhaoming Luo]

Ignoring the return value of mach_port_mod_ref() causes the situation
that when the reference count of the io server port is full, the caller
of dup() still supposes a new file discriptor is allocated. In this
patch we check the return value of mach_port_mod_ref() and return an
error when it fails.

Signed-off-by: Zhaoming Luo <zhmingluo@163.com>
---
 sysdeps/mach/hurd/fcntl.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/sysdeps/mach/hurd/fcntl.c b/sysdeps/mach/hurd/fcntl.c
index a65c190c..d97226cd 100644
--- a/sysdeps/mach/hurd/fcntl.c
+++ b/sysdeps/mach/hurd/fcntl.c
@@ -83,18 +83,34 @@ __libc_fcntl (int fd, int cmd, ...)
 	  result = -1;
 	else
 	  {
-	    /* Give the ports each a user ref for the new descriptor.  */
-	    __mach_port_mod_refs (__mach_task_self (), port,
+	    /* Give the ports (i.e. `ctty` and `port`) each a user ref for
+	       the new descriptor.  */
+	    err = __mach_port_mod_refs (__mach_task_self (), port,
 				  MACH_PORT_RIGHT_SEND, 1);
-	    if (ctty != MACH_PORT_NULL)
-	      __mach_port_mod_refs (__mach_task_self (), ctty,
-				    MACH_PORT_RIGHT_SEND, 1);
-
-	    /* Install the ports and flags in the new descriptor.  */
-	    if (ctty != MACH_PORT_NULL)
-	      _hurd_port_set (&new->ctty, ctty);
-	    new->flags = flags;
-	    _hurd_port_locked_set (&new->port, port); /* Unlocks NEW.  */
+
+	    if (err)
+	      {
+		/* When an error occurs during giving a user ref to the
+		   io server port */
+	        result = -1;
+
+		if (err == KERN_UREFS_OVERFLOW)
+		  errno = EMFILE;
+		else
+		  errno = EINVAL;
+	      }
+	    else
+	      {
+		if (ctty != MACH_PORT_NULL)
+		  __mach_port_mod_refs (__mach_task_self (), ctty,
+			  MACH_PORT_RIGHT_SEND, 1);
+
+		/* Install the ports and flags in the new descriptor.  */
+		if (ctty != MACH_PORT_NULL)
+		  _hurd_port_set (&new->ctty, ctty);
+		new->flags = flags;
+		_hurd_port_locked_set (&new->port, port); /* Unlocks NEW.  */
+	      }
 	  }
 
 	HURD_CRITICAL_END;
-- 
2.47.2