From owner-freebsd-bugs  Tue Mar  9 21:40:16 1999
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Date: 10 Mar 1999 05:28:00 -0000
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Subject: kern/10520: can't exec files under nullfs
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>Number:         10520
>Category:       kern
>Synopsis:       can't exec files under nullfs
>Confidential:   no
>Severity:       critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Mar  9 21:40:01 PST 1999
>Closed-Date:
>Last-Modified:
>Originator:     Bill Trost
>Release:        FreeBSD 4.0-CURRENT i386
>Organization:
Trost Computing
>Environment:

Pentium-class machine, nullfs as a loadable kernel module, cvsup'd as
of the afternoon (PST) of 3/8/1999.  I don't know what else you might want,
but I have RCS'd a copy of the kernel config in case that would be useful.

>Description:

Exec'ing programs via a nullfs mount can result in the program not
running or the OS crashing.

>How-To-Repeat:

Two different failure modes:

	for d in src obj; do mount -t null /mnt/usr/$d /usr/$d; done
	cd /usr/src
	make buildworld

"make buildworld" fails when it first tries to execute the bootstrap make,
to the tune of the make program not being in the right format.

The more dramatic failure is accomplished by:

	mount /tmp/foo /tmp/bar
	cp /usr/bin/true /tmp/bar/
	/tmp/bar/true

This causes a kernel page fault:

	fault addr = 0x40
	fault code = supervisor read, page not present
	interrupt mask = net bio cam
	trap # = 12

ddb traceback says:

	ffs_getpages + 0x108
	_end at 0xf07944b5
	vnode_pager_getpages
	exec_map_first_page
	execve
	syscall

I can provide more detail if that would be useful.

>Fix:
	
Nothing beyond "Don't do that."


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


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