kern/55993: getcwd() breaks on unionfs mounted directories

[Ulrich Spoerlein]

>Number:         55993
>Category:       kern
>Synopsis:       getcwd() breaks on unionfs mounted directories
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Aug 26 07:00:26 PDT 2003
>Closed-Date:
>Last-Modified:
>Originator:     Ulrich Spoerlein
>Release:        FreeBSD 5.1-RELEASE i386
>Organization:
>Environment:
System: FreeBSD roadrunner 5.1-RELEASE FreeBSD 5.1-RELEASE #1: Mon Aug 11 15:27:16 CEST 2003 q at roadrunner:/usr/obj/usr/src/sys/ROADRUNNER i386
>Description:
Inside a chroot, a simple 'pwd' will fail, if it is run on a unionfs mounted
directory. truss shows the following:
readlink("/etc/malloc.conf","aj",63)             = 2 (0x2)
issetugid()                                      = 0 (0x0)
getuid()                                         = 0 (0x0)
mmap(0x0,4096,0x3,0x1002,-1,0x0)                 = 671449088 (0x28058000)
break(0x805c000)                                 = 0 (0x0)
break(0x805d000)                                 = 0 (0x0)
__getcwd(0x805c000,0x3fc)                        ERR#20 'Not a directory'
stat("/",0xbfbff4e0)                             = 0 (0x0)
lstat(".",0xbfbff4e0)                            = 0 (0x0)
stat("..",0xbfbff400)                            = 0 (0x0)
open("..",0x4,00)                                = 3 (0x3)
fstat(3,0xbfbff400)                              = 0 (0x0)
fcntl(0x3,0x2,0x1)                               = 0 (0x0)
break(0x805e000)                                 = 0 (0x0)
__sysctl(0xbfbff2b0,0x2,0x8059084,0xbfbff2ac,0x0,0x0) = 0 (0x0)
fstatfs(0x3,0xbfbff300)                          = 0 (0x0)
break(0x805f000)                                 = 0 (0x0)
getdirentries(0x3,0x805e000,0x1000,0x805d014)    = 512 (0x200)
getdirentries(0x3,0x805e200,0xe00,0x805d014)     = 512 (0x200)
getdirentries(0x3,0x805e400,0xc00,0x805d014)     = 0 (0x0)
fstat(3,0xbfbff4e0)                              = 0 (0x0)
lseek(3,0x200,0)                                 = 512 (0x200)
close(3)                                         = 0 (0x0)
lstat("../",0xbfbff4e0)                          = 0 (0x0)
stat("../..",0xbfbff400)                         = 0 (0x0)
open("../..",0x4,04)                             = 3 (0x3)
fstat(3,0xbfbff400)                              = 0 (0x0)
fcntl(0x3,0x2,0x1)                               = 0 (0x0)
fstatfs(0x3,0xbfbff300)                          = 0 (0x0)
fstat(3,0xbfbff4e0)                              = 0 (0x0)
getdirentries(0x3,0x805e000,0x1000,0x805d014)    = 512 (0x200)
getdirentries(0x3,0x805e000,0x1000,0x805d014)    = 0 (0x0)
lseek(3,0x0,0)                                   = 0 (0x0)
close(3)                                         = 0 (0x0)
pwd: write(2,0xbfbfedd0,5)                               = 5 (0x5)
.write(2,0xbfbfedf0,1)                           = 1 (0x1)
: write(2,0x80568cc,2)                           = 2 (0x2)
No such file or directory
write(2,0xbfbfedd0,26)                           = 26 (0x1a)
exit(0x1)
process exit, rval = 256

This also renders 'make' in any port of choice unuseable.
>How-To-Repeat:
cd /usr/src && make world DESTDIR=/livefs
mkdir -p /livefs/usr/ports && mount -t unionfs /usr/ports /livefs/usr/ports

Doing a pwd in /livefs/usr/ports/editors/vim works just fine, however doing a
'make' fails. Running truss on both processes shows that both processes should
fail to get getcwd(). I don't know why a simple pwd prints the correct directory,
a 'truss pwd' does not.

Now chroot to /livefs

# chroot /livefs /bin/tcsh
# cd /usr/ports/editors/vim && pwd
pwd: .: No such file or directory

So here pwd "correctly fails" to call getcwd() (It always returns ERR#20), make is
broken too.

>Fix:

Please don't tell me that unionfs is buggy, I know that and I read the manpages.
However I think that (when working) unionfs is a real cool tool and can obviously
do more than an union-mount. I will try to get into debugging this, but my skills
are severly limited with respect to that area :(

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