Fix for the panic("vm_thread_new: kstack allocation failed") and

silent NULL pointer dereference in the i386 and sparc64 pmap_pinit()
when the kmem_alloc_nofault() failed to allocate address space. Both
functions now return error instead of panicing or dereferencing NULL.

As consequence, vmspace_exec() and vmspace_unshare() returns the errno
int. struct vmspace arg was added to vm_forkproc() to avoid dealing
with failed allocation when most of the fork1() job is already done.

The kernel stack for the thread is now set up in the thread_alloc(),
that itself may return NULL. Also, allocation of the first process
thread is performed in the fork1() to properly deal with stack
allocation failure. proc_linkup() is separated into proc_linkup()
called from fork1(), and proc_linkup0(), that is used to set up the
kernel process (was known as swapper).

In collaboration with:	Peter Holm
Reviewed by:	jhb

1 files changed, 34 insertions, 7 deletions

diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 917de57..ab7ca8b 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -195,6 +195,7 @@ fork1(td, flags, pages, procp)
 	struct filedesc_to_leader *fdtol;
 	struct thread *td2;
 	struct sigacts *newsigacts;
+	struct vmspace *vm2;
 	int error;
 
 	/* Can't copy and clear. */
@@ -218,7 +219,9 @@ fork1(td, flags, pages, procp)
 			PROC_UNLOCK(p1);
 		}
 
-		vm_forkproc(td, NULL, NULL, flags);
+		error = vm_forkproc(td, NULL, NULL, NULL, flags);
+		if (error)
+			goto norfproc_fail;
 
 		/*
 		 * Close all file descriptors.
@@ -236,6 +239,7 @@ fork1(td, flags, pages, procp)
 		if (flags & RFFDG) 
 			fdunshare(p1, td);
 
+norfproc_fail:
 		if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
 		    (flags & (RFCFDG | RFFDG))) {
 			PROC_LOCK(p1);
@@ -243,7 +247,7 @@ fork1(td, flags, pages, procp)
 			PROC_UNLOCK(p1);
 		}
 		*procp = NULL;
-		return (0);
+		return (error);
 	}
 
 	/*
@@ -254,6 +258,32 @@ fork1(td, flags, pages, procp)
 
 	/* Allocate new proc. */
 	newproc = uma_zalloc(proc_zone, M_WAITOK);
+	if (TAILQ_EMPTY(&newproc->p_threads)) {
+		td2 = thread_alloc();
+		if (td2 == NULL) {
+			error = ENOMEM;
+			goto fail1;
+		}
+		proc_linkup(newproc, td2);
+		sched_newproc(newproc, td2);
+	} else
+		td2 = FIRST_THREAD_IN_PROC(newproc);
+
+	/* Allocate and switch to an alternate kstack if specified. */
+	if (pages != 0) {
+		if (!vm_thread_new_altkstack(td2, pages)) {
+			error = ENOMEM;
+			goto fail1;
+		}
+	}
+	if ((flags & RFMEM) == 0) {
+		vm2 = vmspace_fork(p1->p_vmspace);
+		if (vm2 == NULL) {
+			error = ENOMEM;
+			goto fail1;
+		}
+	} else
+		vm2 = NULL;
 #ifdef MAC
 	mac_proc_init(newproc);
 #endif
@@ -380,7 +410,6 @@ again:
 		lastpid = trypid;
 
 	p2 = newproc;
-	td2 = FIRST_THREAD_IN_PROC(newproc);
 	p2->p_state = PRS_NEW;		/* protect against others */
 	p2->p_pid = trypid;
 	/*
@@ -456,9 +485,6 @@ again:
 	 * Start by zeroing the section of proc that is zero-initialized,
 	 * then copy the section that is copied directly from the parent.
 	 */
-	/* Allocate and switch to an alternate kstack if specified. */
-	if (pages != 0)
-		vm_thread_new_altkstack(td2, pages);
 
 	PROC_LOCK(p2);
 	PROC_LOCK(p1);
@@ -630,7 +656,7 @@ again:
 	 * Finish creating the child process.  It will return via a different
 	 * execution path later.  (ie: directly into user mode)
 	 */
-	vm_forkproc(td, p2, td2, flags);
+	vm_forkproc(td, p2, td2, vm2, flags);
 
 	if (flags == (RFFDG | RFPROC)) {
 		PCPU_INC(cnt.v_forks);
@@ -713,6 +739,7 @@ fail:
 #ifdef MAC
 	mac_proc_destroy(newproc);
 #endif
+fail1:
 	uma_zfree(proc_zone, newproc);
 	pause("fork", hz / 2);
 	return (error);