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Date:      Tue, 14 Jul 2015 02:00:51 +0000 (UTC)
From:      "Conrad E. Meyer" <cem@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r285522 - in head/sys: kern sys
Message-ID:  <201507140200.t6E20pxT032688@repo.freebsd.org>
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Author: cem
Date: Tue Jul 14 02:00:50 2015
New Revision: 285522
URL: https://svnweb.freebsd.org/changeset/base/285522

Log:
  Fix cleanup race between unp_dispose and unp_gc
  
  unp_dispose and unp_gc could race to teardown the same mbuf chains, which
  can lead to dereferencing freed filedesc pointers.
  
  This patch adds an IGNORE_RIGHTS flag on unpcbs marking the unpcb's RIGHTS
  as invalid/freed. The flag is protected by UNP_LIST_LOCK.
  
  To serialize against unp_gc, unp_dispose needs the socket object. Change the
  dom_dispose() KPI to take a socket object instead of an mbuf chain directly.
  
  PR:		194264
  Differential Revision:	https://reviews.freebsd.org/D3044
  Reviewed by:	mjg (earlier version)
  Approved by:	markj (mentor)
  Obtained from:	mjg
  MFC after:	1 month
  Sponsored by:	EMC / Isilon Storage Division

Modified:
  head/sys/kern/uipc_socket.c
  head/sys/kern/uipc_usrreq.c
  head/sys/sys/domain.h
  head/sys/sys/unpcb.h

Modified: head/sys/kern/uipc_socket.c
==============================================================================
--- head/sys/kern/uipc_socket.c	Tue Jul 14 01:32:25 2015	(r285521)
+++ head/sys/kern/uipc_socket.c	Tue Jul 14 02:00:50 2015	(r285522)
@@ -805,7 +805,7 @@ sofree(struct socket *so)
 
 	VNET_SO_ASSERT(so);
 	if (pr->pr_flags & PR_RIGHTS && pr->pr_domain->dom_dispose != NULL)
-		(*pr->pr_domain->dom_dispose)(so->so_rcv.sb_mb);
+		(*pr->pr_domain->dom_dispose)(so);
 	if (pr->pr_usrreqs->pru_detach != NULL)
 		(*pr->pr_usrreqs->pru_detach)(so);
 
@@ -2356,7 +2356,7 @@ sorflush(struct socket *so)
 {
 	struct sockbuf *sb = &so->so_rcv;
 	struct protosw *pr = so->so_proto;
-	struct sockbuf asb;
+	struct socket aso;
 
 	VNET_SO_ASSERT(so);
 
@@ -2381,8 +2381,9 @@ sorflush(struct socket *so)
 	 * and mutex data unchanged.
 	 */
 	SOCKBUF_LOCK(sb);
-	bzero(&asb, offsetof(struct sockbuf, sb_startzero));
-	bcopy(&sb->sb_startzero, &asb.sb_startzero,
+	bzero(&aso, sizeof(aso));
+	aso.so_pcb = so->so_pcb;
+	bcopy(&sb->sb_startzero, &aso.so_rcv.sb_startzero,
 	    sizeof(*sb) - offsetof(struct sockbuf, sb_startzero));
 	bzero(&sb->sb_startzero,
 	    sizeof(*sb) - offsetof(struct sockbuf, sb_startzero));
@@ -2390,12 +2391,12 @@ sorflush(struct socket *so)
 	sbunlock(sb);
 
 	/*
-	 * Dispose of special rights and flush the socket buffer.  Don't call
-	 * any unsafe routines (that rely on locks being initialized) on asb.
+	 * Dispose of special rights and flush the copied socket.  Don't call
+	 * any unsafe routines (that rely on locks being initialized) on aso.
 	 */
 	if (pr->pr_flags & PR_RIGHTS && pr->pr_domain->dom_dispose != NULL)
-		(*pr->pr_domain->dom_dispose)(asb.sb_mb);
-	sbrelease_internal(&asb, so);
+		(*pr->pr_domain->dom_dispose)(&aso);
+	sbrelease_internal(&aso.so_rcv, so);
 }
 
 /*

Modified: head/sys/kern/uipc_usrreq.c
==============================================================================
--- head/sys/kern/uipc_usrreq.c	Tue Jul 14 01:32:25 2015	(r285521)
+++ head/sys/kern/uipc_usrreq.c	Tue Jul 14 02:00:50 2015	(r285522)
@@ -278,6 +278,7 @@ static int	unp_connectat(int, struct soc
 static int	unp_connect2(struct socket *so, struct socket *so2, int);
 static void	unp_disconnect(struct unpcb *unp, struct unpcb *unp2);
 static void	unp_dispose(struct mbuf *);
+static void	unp_dispose_so(struct socket *so);
 static void	unp_shutdown(struct unpcb *);
 static void	unp_drop(struct unpcb *, int);
 static void	unp_gc(__unused void *, int);
@@ -334,7 +335,7 @@ static struct domain localdomain = {
 	.dom_name =		"local",
 	.dom_init =		unp_init,
 	.dom_externalize =	unp_externalize,
-	.dom_dispose =		unp_dispose,
+	.dom_dispose =		unp_dispose_so,
 	.dom_protosw =		localsw,
 	.dom_protoswNPROTOSW =	&localsw[sizeof(localsw)/sizeof(localsw[0])]
 };
@@ -2216,15 +2217,19 @@ unp_gc_process(struct unpcb *unp)
 	 * Mark all sockets we reference with RIGHTS.
 	 */
 	so = unp->unp_socket;
-	SOCKBUF_LOCK(&so->so_rcv);
-	unp_scan(so->so_rcv.sb_mb, unp_accessable);
-	SOCKBUF_UNLOCK(&so->so_rcv);
+	if ((unp->unp_gcflag & UNPGC_IGNORE_RIGHTS) == 0) {
+		SOCKBUF_LOCK(&so->so_rcv);
+		unp_scan(so->so_rcv.sb_mb, unp_accessable);
+		SOCKBUF_UNLOCK(&so->so_rcv);
+	}
 
 	/*
 	 * Mark all sockets in our accept queue.
 	 */
 	ACCEPT_LOCK();
 	TAILQ_FOREACH(soa, &so->so_comp, so_list) {
+		if ((sotounpcb(soa)->unp_gcflag & UNPGC_IGNORE_RIGHTS) != 0)
+			continue;
 		SOCKBUF_LOCK(&soa->so_rcv);
 		unp_scan(soa->so_rcv.sb_mb, unp_accessable);
 		SOCKBUF_UNLOCK(&soa->so_rcv);
@@ -2254,11 +2259,13 @@ unp_gc(__unused void *arg, int pending)
 	unp_taskcount++;
 	UNP_LIST_LOCK();
 	/*
-	 * First clear all gc flags from previous runs.
+	 * First clear all gc flags from previous runs, apart from
+	 * UNPGC_IGNORE_RIGHTS.
 	 */
 	for (head = heads; *head != NULL; head++)
 		LIST_FOREACH(unp, *head, unp_link)
-			unp->unp_gcflag = 0;
+			unp->unp_gcflag =
+			    (unp->unp_gcflag & UNPGC_IGNORE_RIGHTS);
 
 	/*
 	 * Scan marking all reachable sockets with UNPGC_REF.  Once a socket
@@ -2335,6 +2342,21 @@ unp_dispose(struct mbuf *m)
 		unp_scan(m, unp_freerights);
 }
 
+/*
+ * Synchronize against unp_gc, which can trip over data as we are freeing it.
+ */
+static void
+unp_dispose_so(struct socket *so)
+{
+	struct unpcb *unp;
+
+	unp = sotounpcb(so);
+	UNP_LIST_LOCK();
+	unp->unp_gcflag |= UNPGC_IGNORE_RIGHTS;
+	UNP_LIST_UNLOCK();
+	unp_dispose(so->so_rcv.sb_mb);
+}
+
 static void
 unp_scan(struct mbuf *m0, void (*op)(struct filedescent **, int))
 {

Modified: head/sys/sys/domain.h
==============================================================================
--- head/sys/sys/domain.h	Tue Jul 14 01:32:25 2015	(r285521)
+++ head/sys/sys/domain.h	Tue Jul 14 02:00:50 2015	(r285522)
@@ -42,6 +42,7 @@
  */
 struct	mbuf;
 struct	ifnet;
+struct	socket;
 
 struct domain {
 	int	dom_family;		/* AF_xxx */
@@ -53,7 +54,7 @@ struct domain {
 	int	(*dom_externalize)	/* externalize access rights */
 		(struct mbuf *, struct mbuf **, int);
 	void	(*dom_dispose)		/* dispose of internalized rights */
-		(struct mbuf *);
+		(struct socket *);
 	struct	protosw *dom_protosw, *dom_protoswNPROTOSW;
 	struct	domain *dom_next;
 	int	(*dom_rtattach)		/* initialize routing table */

Modified: head/sys/sys/unpcb.h
==============================================================================
--- head/sys/sys/unpcb.h	Tue Jul 14 01:32:25 2015	(r285521)
+++ head/sys/sys/unpcb.h	Tue Jul 14 02:00:50 2015	(r285522)
@@ -106,6 +106,7 @@ struct unpcb {
 #define	UNPGC_REF			0x1	/* unpcb has external ref. */
 #define	UNPGC_DEAD			0x2	/* unpcb might be dead. */
 #define	UNPGC_SCANNED			0x4	/* Has been scanned. */
+#define	UNPGC_IGNORE_RIGHTS		0x8	/* Attached rights are freed */
 
 /*
  * These flags are used to handle non-atomicity in connect() and bind()

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