[krbdev.mit.edu #8766] ksu sets KRB5CCNAME to MEMORY:_ksu when using switchable default cache

Hi,

When the default cache is a switchable one, e.g. KEYRING, as set by...

[libdefaults]
 default_ccache_name = KEYRING:persistent:%{uid}

...  using ksu will result in KRB5CCNAME being set to MEMORY:_ksu and
having no credentials:

[bolt]toby: ksu . -n toby/root 
WARNING: Your password may be exposed if you enter it here and are logged
        in remotely using an unsecure (non-encrypted) channel.
Kerberos password for toby/[email protected]: : 
Leaving uid as toby (xxxxx)
[bolt]toby: klist
klist: No credentials cache found
[bolt]toby: echo $KRB5CCNAME
MEMORY:_ksu
[bolt]toby: 

This seems to happen in src/clients/ksu/main.c:resolve_target_cache...

The check to determine if the cache type is switchable resolves to true
and the subsequent call to krb5_cc_resolve_cache_match seems to match
on the 'MEMORY:_ksu' cache as used internally by ksu, hence this cache is
returned.

Note this is running the os-shipped 1.15.1 on Scientific Linux 7.5.  It
doesn't appear that the relevant code has subsequently changed (in 1.16.2)
but I can't easily test the behaviour.

Cheers
Toby


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