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Date: Thu, 30 Nov 2000 05:30:53 -0800 (PST)
From: tmoestl@gmx.net
To: freebsd-gnats-submit@FreeBSD.org
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Subject: kern/23191: [PATCH] Fix for panics in lookup() after forced unmount
Sender: owner-freebsd-bugs@FreeBSD.ORG
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>Number:         23191
>Category:       kern
>Synopsis:       [PATCH] Fix for panics in lookup() after forced unmount
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Nov 30 05:40:00 PST 2000
>Closed-Date:
>Last-Modified:
>Originator:     Thomas Moestl
>Release:        FreeBSD 4.2-STABLE
>Organization:
>Environment:
FreeBSD crow.local 4.2-STABLE FreeBSD 4.2-STABLE #19: Sun Nov 26 01:04:14 CET 2000     root@crow.local:/usr/src/sys/compile/CROW  i386
>Description:
This is a fix for a problem described in PR kern/19572. It was
recently discussed at -hackers. The problem is a null-pointer 
dereference that happens in kern/vfs_lookup.c when accessing ".." 
with a v_mount entry for the current directory vnode of NULL. This 
happens when a volume is forcibly unmounted, and the vnode for a 
working directory in the mounted volume is cleared.
>How-To-Repeat:
cd into a mountpoint, forcibly unmount the volume, and try to access "..":

mount /cdrom
cd /cdrom
umount -f /cdrom
ls ..

>Fix:
The following patch should fix the problem, as discussed on -hackers.
It is against 4.2-STABLE, but it applies (with minor offsets) to -CURRENT,
and there seems to not have changed anything that could make the patch
break. If this gets mangled, the patch is also at
http://home.t-online.de/home/Moestl/lookup-dotdot.diff

*** old/kern/vfs_lookup.c	Sat Nov 25 23:55:39 2000
--- new/kern/vfs_lookup.c	Sun Nov 26 00:58:15 2000
***************
*** 403,408 ****
--- 403,412 ----
  			if ((dp->v_flag & VROOT) == 0 ||
  			    (cnp->cn_flags & NOCROSSMOUNT))
  				break;
+ 			if (dp->v_mount == NULL) {	/* forced unmount */
+ 				error = EBADF;
+ 				goto bad;
+ 			}
  			tdp = dp;
  			dp = dp->v_mount->mnt_vnodecovered;
  			vput(tdp);
***************
*** 424,430 ****
  		printf("not found\n");
  #endif
  		if ((error == ENOENT) &&
! 		    (dp->v_flag & VROOT) &&
  		    (dp->v_mount->mnt_flag & MNT_UNION)) {
  			tdp = dp;
  			dp = dp->v_mount->mnt_vnodecovered;
--- 428,434 ----
  		printf("not found\n");
  #endif
  		if ((error == ENOENT) &&
! 		    (dp->v_flag & VROOT) && (dp->v_mount != NULL) &&
  		    (dp->v_mount->mnt_flag & MNT_UNION)) {
  			tdp = dp;
  			dp = dp->v_mount->mnt_vnodecovered;
***************
*** 502,507 ****
--- 506,517 ----
  	    ((cnp->cn_flags & FOLLOW) || trailing_slash ||
  	     *ndp->ni_next == '/')) {
  		cnp->cn_flags |= ISSYMLINK;
+ 		if (dp->v_mount == NULL) {
+ 			/* We can't know whether the directory was mounted with
+ 			 * NOSYMFOLLOW, so we can't follow safely. */
+ 			error = EBADF;
+ 			goto bad2;
+ 		}
  		if (dp->v_mount->mnt_flag & MNT_NOSYMFOLLOW) {
  			error = EACCES;
  			goto bad2;


>Release-Note:
>Audit-Trail:
>Unformatted:


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