Re: Text file busy

Terry Lambert wrote:

>Wesley Morgan wrote:
>  
>
>>It's also unfortunate that this protection does not seem to extend to
>>libaries. I've had some in-use X libraries get overwritten with some very
>>colorful results.
>>    
>>
>
>So send patches.
>  
>
I did a year ago :-) See PR 37554. (Not the original patch, the 
self-follow-up).

That was for 4.5-STABLE: It's been running on a box that does nightly 
builds of -current and -stable (and infrequent installworlds of -stable) 
since then without any ill effects. A -current equivalent (with a sysctl 
knob, "vm.mmap_exec_immutable", to turn the behaviour on/off) is 
attached, in case anyone's interested.

As noted in the original PR, the choice of PROT_EXEC to decide to add 
VV_TEXT to the vnode might be better done with a new mmap flag, say, 
PROT_IMMUTABLE or something, but PROT_EXEC works fine for me.


Index: sys/vm/vm_mmap.c
===================================================================
RCS file: /pub/FreeBSD/development/FreeBSD-CVS/src/sys/vm/vm_mmap.c,v
retrieving revision 1.165
diff -u -r1.165 vm_mmap.c
--- sys/vm/vm_mmap.c	7 Sep 2003 18:47:54 -0000	1.165
+++ sys/vm/vm_mmap.c	15 Sep 2003 13:36:46 -0000
_at__at_ -91,6 +91,11 _at__at_
 static int max_proc_mmap;
 SYSCTL_INT(_vm, OID_AUTO, max_proc_mmap, CTLFLAG_RW, &max_proc_mmap, 0, "");
 
+static int mmap_exec_immutable = 1;
+SYSCTL_INT(_vm, OID_AUTO, mmap_exec_immutable, CTLFLAG_RW,
+    &mmap_exec_immutable, 1, "mmap(2) of a regular file for execute access "
+    "marks the file as immutable");
+
 /*
  * Set the maximum number of vm_map_entry structures per process.  Roughly
  * speaking vm_map_entry structures are tiny, so allowing them to eat 1/100
_at__at_ -443,8 +448,18 _at__at_
 		error = vm_mmap(&vms->vm_map, &addr, size, prot, maxprot,
 		    flags, handle, pos);
 	mtx_lock(&Giant);
-	if (error == 0)
+	if (error == 0) {
+		/*
+		 * If mapping a regular file as PROT_EXEC, and configured to,
+		 * mark the file as immutable
+		 */
+		if (mmap_exec_immutable &&
+		    handle != NULL && vp != NULL &&
+		    (prot & PROT_EXEC) && vp->v_type == VREG)
+			vp->v_vflag |= VV_TEXT;
 		td->td_retval[0] = (register_t) (addr + pageoff);
+	}
+
 done:
 	if (vp)
 		vput(vp);