kernel: fix multiple devproc bugs and pid reuse issues

devproc assumes that when we hold the Proc.debug qlock,
the process will be prevented from exiting. but there is
another race where the process has already exited and
the Proc* slot gets reused. to solve this, on process
creation we also have to acquire the debug qlock while
initializing the fields of the process. this also means
newproc() should only initialize fields *not* protected
by the debug qlock.

always acquire the Proc.debug qlock when changing strings
in the proc structure to avoid doublefree on concurrent
update. for changing the user string, we add a procsetuser()
function that does this for auth.c and devcap.

remove pgrpnote() from pgrp.c and replace by static
postnotepg() in devproc.

avoid the assumption that the Proc* entries returned by
proctab() are continuous.

fixed devproc permission issues:
	- make sure only eve can access /proc/trace
	- none should only be allowed to read its own /proc/n/text
	- move Proc.kp checks into procopen()

pid reuse was not handled correctly, as we where only
checking if a pid had a living process, but there still
could be processes expecting a particular parentpid or
noteid.

this is now addressed with reference counted Pid
structures which are organized in a hash table.
read access to the hash table does not require locks
which will be usefull for dtracy later.

1 files changed, 9 insertions, 7 deletions

diff --git a/sys/src/9/port/portdat.h b/sys/src/9/port/portdat.h
index 2a1cd3b07..7c9aa7193 100644
--- a/sys/src/9/port/portdat.h
+++ b/sys/src/9/port/portdat.h
@@ -187,7 +187,6 @@ struct Chan
 	Mnt*	mux;			/* Mnt for clients using me for messages */
 	union {
 		void*	aux;
-		Qid	pgrpid;		/* for #p/notepg */
 		ulong	mid;		/* for ns in devproc */
 	};
 	Chan*	mchan;			/* channel to mounted server */
@@ -649,28 +648,31 @@ struct Proc
 	Mach	*mach;		/* machine running this proc */
 	char	*text;
 	char	*user;
+
 	char	*args;
 	int	nargs;		/* number of bytes of args */
 	int	setargs;	/* process changed its args */
+
 	Proc	*rnext;		/* next process in run queue */
 	Proc	*qnext;		/* next process on queue for a QLock */
-	QLock	*qlock;		/* addr of qlock being queued for DEBUG */
-	int	state;
+
 	char	*psstate;	/* What /proc/#/status reports */
-	Segment	*seg[NSEG];
-	QLock	seglock;	/* locked whenever seg[] changes */
+	int	state;
+
 	ulong	pid;
 	ulong	noteid;		/* Equivalent of note group */
 	ulong	parentpid;
-	Proc	*pidhash;	/* next proc in pid hash */
 
+	Proc	*parent;	/* Process to send wait record on exit */
 	Lock	exl;		/* Lock count and waitq */
 	Waitq	*waitq;		/* Exited processes wait children */
 	int	nchild;		/* Number of living children */
 	int	nwait;		/* Number of uncollected wait records */
 	QLock	qwaitr;
 	Rendez	waitr;		/* Place to hang out in wait */
-	Proc	*parent;
+
+	QLock	seglock;	/* locked whenever seg[] changes */
+	Segment	*seg[NSEG];
 
 	Pgrp	*pgrp;		/* Process group for namespace */
 	Egrp 	*egrp;		/* Environment group */