Is zero a valid value for the pid member of the AUDIT_SIGNAL_INFO message?

[Richard Guy Briggs]

On 14/03/11, Eric Paris wrote:
> On Tue, 2014-03-11 at 18:15 -0400, Richard Guy Briggs wrote:
> > Steve,
> > 
> > Subject says it all...
> > 
> > Is zero a valid value for the pid member of the AUDIT_SIGNAL_INFO message?
> 
> No...
> 
> Given that userspace requests AUDIT_SIGNAL_INFO after it gets a signal,
> and that audit_sig_{uid,pid,...} get filled in when some task sent
> auditd that signal, the idea that the pid would be 0 doesn't make
> sense...  (unless auditd requests AUDIT_SIGNAL_INFO without getting a
> signal, but that's just dumb)

The reason I ask is that it is initialized to -1, which I assume is no
more valid than zero in your interpretation above.

I looked at converting audit_sig_pid from pid_t to struct pid *, but
then get_pid() would also be needed to protect that reference.  A
put_pid() would need to be done once it is no longer needed, which could
be immediately after it is read in the AUDIT_SIGNAL_INFO message
preparation, assuming it would never need to be read again.  If this
isn't the case, put_pid() could be called when audit_pid is nulled, but
if that message never comes, that struct pid is stuck with a stale
refcount.  (That isn't an issue if it is init or systemd, but it is
still wrong.)

This looks more and more like overkill and should probably leave
audit_sig_pid as pid_t.

- RGB

--
Richard Guy Briggs <rbriggs at redhat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
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