Comment 18 for bug 676525

I think I see the source of the problem....

When I do this:

# sudo strace -fo/tmp/a -p $$ &
# sudo mount -t cifs -o username=me,rw,uid=me,gid=mygroup,port=445,sec=krb5,creduid=/tmp/krb5cc_1000 \\\\server.example.com\\home\\me /mnt/me
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
# kill %1
# grep krb5cc /tmp/a
8619 access("/tmp/krb5cc_1000", R_OK) = 0
8619 open("/tmp/krb5cc_1000", O_RDONLY) = 3
# grep ' mount(' /tmp/a
8618 mount("\\\\server.example.com\\home\\me", ".", "cifs", 0, "ip=1.2.3.4,unc=\\\\server.example."...) = -1 EINVAL (Invalid argument)
# dmesg | grep CIFS
[ 4634.121902] CIFS: Unknown mount option "creduid=/tmp/krb5cc_1000"

When I don't used 'creduid=', the mount command returns:
   mount error(126): Required key not available
   Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
and the strace output shows that it doesn't try accessing /tmp/krb5cc_* at all.

When I instead try 'cruid=1000', the same error occurs, and again, no /tmp/krb5cc_* files are being accessed.

In short, I think that either the cifs kernel module needs to allow the creduid option, or the mount.cifs program needs to strip it out before calling mount(). After that, I don't know what else has to happen; perhaps both creduid= and cruid= need to be specified? Or perhaps creduid= needs to be renamed to kccf= (kerberos cached credentials file, a name pulled out of a hat)?

Hopefully someone finally makes cifs+kerberos work from /etc/fstab or /etc/pam.d so that it can be mounted when I log in, without having to enter my password again.

Thanks!