Confusion about process states and invariants

[Pawel Jakub Dawidek]

On Sat, Jun 26, 2004 at 12:38:43PM -0400, Robert Watson wrote:
+> Over the last two weeks, I've seen several reports of panics relating to
+> code making incorrect assumptions about process state, generally relating
+> to the "p_ucred" pointer in new and dying processes.  In particular, a
+> number of pieces of code assume that if a process is reachable by the all
+> process list (or other process lists), p_ucred will be valid and non-NULL
+> if the process lock is held on the process.  This results in possible NULL
+> pointer dereferences in the PRS_NEW state, and also during the tear-down
+> in kern_wait().  At first glance, the easy answer would appear to be
+> "check for p_ucred to be NULL", but I'm actually of the opinion that I'd
+> prefer we have the non-NULL p_ucred invariant actually hold true.  This
+> would permit security checks to be performed properly during those
+> windows.  I'm not very familiar with our process state and locking, but if
+> someone with a more qualified background in that area could comment on the
+> current issue, that would be useful.

Couldn't we move crhold() for p_ucred before it is placed on allproc list?

-- 
Pawel Jakub Dawidek                       http://www.FreeBSD.org
pjd at FreeBSD.org                           http://garage.freebsd.pl
FreeBSD committer                         Am I Evil? Yes, I Am!
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