From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Guy Briggs Subject: Re: Is zero a valid value for the pid member of the AUDIT_SIGNAL_INFO message? Date: Wed, 12 Mar 2014 11:35:56 -0400 Message-ID: <20140312153556.GC15334@madcap2.tricolour.ca> References: <20140311221517.GA15334@madcap2.tricolour.ca> <1394586404.10287.4.camel@localhost> <20140312033201.GC15329@madcap2.tricolour.ca> <2027464.v9FTcEdPSx@x2> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <2027464.v9FTcEdPSx@x2> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-audit-bounces@redhat.com Errors-To: linux-audit-bounces@redhat.com To: Steve Grubb Cc: linux-audit@redhat.com List-Id: linux-audit@redhat.com On 14/03/12, Steve Grubb wrote: > On Tuesday, March 11, 2014 11:32:01 PM Richard Guy Briggs wrote: > > On 14/03/11, Eric Paris wrote: > > > On Tue, 2014-03-11 at 18:15 -0400, Richard Guy Briggs wrote: > > > > 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. > > pid=-1 has a special meaning for signals. But in terms of seeing it in a > sigaction handler for siginfo, not possible. So its a good init value. If you > look at sigaction(2), there is a si_code that indicates why the signal was > sent. One of them is SI_KERNEL. So, its possible that the kernel decides to > send a signal on certain occasions. That message is only sent on request from userspace, so I suppose userspace could request that information at any time, but the only time it would be meaningful is after that userspace process has received a signal. > > 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. > > The code has been working good for a long time. I am wondering if the original > intent was to make it general in case we decided to add more signals that we > are interested in. Such as HUP to reread config or other possibilities? > -Steve - RGB -- Richard Guy Briggs Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat Remote, Ottawa, Canada Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545