[Patch] sys/kern/kern_descrip.c: remove double limit check in fcntl()

[Ed Schouten]

Hello,

I'm working on a project at school to develop a multimedia system (a la
Windows Media Center) based on FreeBSD. I was looking at some code in
sys/kern/kern_descrip.c to figure out how the fcntl() with F_DUPFD and
dup() differ.

I discovered that kern_fcntl() contains some redundant code. Right
before calling do_dup(), it locks the process and checks that the
minimal file descriptor is lower than the limit for the process. The
do_dup() call does exactly the same check almost at the beginning. This
causes the fcntl() call to call PROC_LOCK() once too much.

The patch below prevents this by performing this check by do_dup(). It
will prevent fcntl() from PROC_LOCK()'ing twice. It also fixes the
return value of fcntl(). The manual page states that it should return
EMFILE when it exceeds its limit, though the actual code sets EINVAL.

%%%
--- kern_descrip.c	Thu Nov  9 13:23:40 2006
+++ kern_descrip.c	Thu Nov  9 13:32:28 2006
@@ -355,7 +355,6 @@
 	struct proc *p;
 	char *pop;
 	struct vnode *vp;
-	u_int newmin;
 	int error, flg, tmp;
 	int giant_locked;
 
@@ -393,16 +392,7 @@
 	case F_DUPFD:
 		/* mtx_assert(&Giant, MA_NOTOWNED); */
 		FILEDESC_UNLOCK(fdp);
-		newmin = arg;
-		PROC_LOCK(p);
-		if (newmin >= lim_cur(p, RLIMIT_NOFILE) ||
-		    newmin >= maxfilesperproc) {
-			PROC_UNLOCK(p);
-			error = EINVAL;
-			break;
-		}
-		PROC_UNLOCK(p);
-		error = do_dup(td, DUP_VARIABLE, fd, newmin, td->td_retval);
+		error = do_dup(td, DUP_VARIABLE, fd, arg, td->td_retval);
 		break;
 
 	case F_GETFD:
%%%

-- 
 Ed Schouten <ed at fxq.nl>
 WWW: http://g-rave.nl/
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