pgrp: Prevent use after free.

Often, we have a process locked and need to get locked process group.
In this case, because progress group lock is before process lock,
unlocking process allows the group to be freed.  See for instance
tty_wait_background().

Make pgrp structures allocated from nofree zone, and ensure type stability
of the pgrp mutex.

Reviewed by:	jilles
Tested by:	pho
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D27871

1 files changed, 15 insertions, 5 deletions

diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c
index ea34631995b1..fab1df795799 100644
--- a/sys/kern/kern_proc.c
+++ b/sys/kern/kern_proc.c
@@ -98,7 +98,6 @@ __FBSDID("$FreeBSD$");
 
 SDT_PROVIDER_DEFINE(proc);
 
-MALLOC_DEFINE(M_PGRP, "pgrp", "process group header");
 MALLOC_DEFINE(M_SESSION, "session", "session header");
 static MALLOC_DEFINE(M_PROC, "proc", "Proc structures");
 MALLOC_DEFINE(M_SUBPROC, "subproc", "Proc sub-structures");
@@ -112,6 +111,7 @@ static void fill_kinfo_thread(struct thread *td, struct kinfo_proc *kp,
     int preferthread);
 static void pgadjustjobc(struct pgrp *pgrp, bool entering);
 static void pgdelete(struct pgrp *);
+static int pgrp_init(void *mem, int size, int flags);
 static int proc_ctor(void *mem, int size, void *arg, int flags);
 static void proc_dtor(void *mem, int size, void *arg);
 static int proc_init(void *mem, int size, int flags);
@@ -133,6 +133,7 @@ struct sx __exclusive_cache_line proctree_lock;
 struct mtx __exclusive_cache_line ppeers_lock;
 struct mtx __exclusive_cache_line procid_lock;
 uma_zone_t proc_zone;
+uma_zone_t pgrp_zone;
 
 /*
  * The offset of various fields in struct proc and struct thread.
@@ -196,6 +197,8 @@ procinit(void)
 	proc_zone = uma_zcreate("PROC", sched_sizeof_proc(),
 	    proc_ctor, proc_dtor, proc_init, proc_fini,
 	    UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
+	pgrp_zone = uma_zcreate("PGRP", sizeof(struct pgrp), NULL, NULL,
+	    pgrp_init, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
 	uihashinit();
 }
 
@@ -299,6 +302,16 @@ proc_fini(void *mem, int size)
 #endif
 }
 
+static int
+pgrp_init(void *mem, int size, int flags)
+{
+	struct pgrp *pg;
+
+	pg = mem;
+	mtx_init(&pg->pg_mtx, "process group", NULL, MTX_DEF | MTX_DUPOK);
+	return (0);
+}
+
 /*
  * PID space management.
  *
@@ -570,8 +583,6 @@ enterpgrp(struct proc *p, pid_t pgid, struct pgrp *pgrp, struct session *sess)
 	KASSERT(!SESS_LEADER(p),
 	    ("enterpgrp: session leader attempted setpgrp"));
 
-	mtx_init(&pgrp->pg_mtx, "process group", NULL, MTX_DEF | MTX_DUPOK);
-
 	if (sess != NULL) {
 		/*
 		 * new session
@@ -798,8 +809,7 @@ pgdelete(struct pgrp *pgrp)
 	}
 
 	proc_id_clear(PROC_ID_GROUP, pgrp->pg_id);
-	mtx_destroy(&pgrp->pg_mtx);
-	free(pgrp, M_PGRP);
+	uma_zfree(pgrp_zone, pgrp);
 	sess_release(savesess);
 }