wait4(2)/waitid(2): separate copying rusage to userland

New helpers: kernel_waitid() and kernel_wait4().  sys_waitid(),
sys_wait4() and their compat variants switched to those.  Copying
struct rusage to userland is left to syscall itself.  For
compat_sys_wait4() that eliminates the use of set_fs() completely.
For compat_sys_waitid() it's still needed (for siginfo handling);
that will change shortly.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/resource.h

@@ -6,7 +6,7 @@
 
 struct task_struct;
 
-int getrusage(struct task_struct *p, int who, struct rusage __user *ru);
+void getrusage(struct task_struct *p, int who, struct rusage *ru);
 int do_prlimit(struct task_struct *tsk, unsigned int resource,
 		struct rlimit *new_rlim, struct rlimit *old_rlim);
 

kernel/exit.c

@@ -1003,7 +1003,7 @@ struct wait_opts {
 
 	struct siginfo __user	*wo_info;
 	int __user		*wo_stat;
-	struct rusage __user	*wo_rusage;
+	struct rusage		*wo_rusage;
 
 	wait_queue_t		child_wait;
 	int			notask_error;
@@ -1054,8 +1054,10 @@ static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
 				pid_t pid, uid_t uid, int why, int status)
 {
 	struct siginfo __user *infop;
-	int retval = wo->wo_rusage
-		? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
+	int retval = 0;
+
+	if (wo->wo_rusage)
+		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
 
 	put_task_struct(p);
 	infop = wo->wo_info;
@@ -1182,8 +1184,9 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
 		spin_unlock_irq(&current->sighand->siglock);
 	}
 
-	retval = wo->wo_rusage
-		? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
+	if (wo->wo_rusage)
+		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
+	retval = 0;
 	status = (p->signal->flags & SIGNAL_GROUP_EXIT)
 		? p->signal->group_exit_code : p->exit_code;
 	if (!retval && wo->wo_stat)
@@ -1316,8 +1319,9 @@ static int wait_task_stopped(struct wait_opts *wo,
 	if (unlikely(wo->wo_flags & WNOWAIT))
 		return wait_noreap_copyout(wo, p, pid, uid, why, exit_code);
 
-	retval = wo->wo_rusage
-		? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
+	if (wo->wo_rusage)
+		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
+	retval = 0;
 	if (!retval && wo->wo_stat)
 		retval = put_user((exit_code << 8) | 0x7f, wo->wo_stat);
 
@@ -1377,8 +1381,9 @@ static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
 	sched_annotate_sleep();
 
 	if (!wo->wo_info) {
-		retval = wo->wo_rusage
-			? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
+		if (wo->wo_rusage)
+			getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
+		retval = 0;
 		put_task_struct(p);
 		if (!retval && wo->wo_stat)
 			retval = put_user(0xffff, wo->wo_stat);
@@ -1618,8 +1623,8 @@ static long do_wait(struct wait_opts *wo)
 	return retval;
 }
 
-SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
-		infop, int, options, struct rusage __user *, ru)
+static long kernel_waitid(int which, pid_t upid, struct siginfo __user *infop,
+			  int options, struct rusage *ru)
 {
 	struct wait_opts wo;
 	struct pid *pid = NULL;
@@ -1687,8 +1692,21 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
 	return ret;
 }
 
-SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
-		int, options, struct rusage __user *, ru)
+SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
+		infop, int, options, struct rusage __user *, ru)
+{
+	struct rusage r;
+	long err = kernel_waitid(which, upid, infop, options, ru ? &r : NULL);
+
+	if (!err) {
+		if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
+			return -EFAULT;
+	}
+	return err;
+}
+
+static long kernel_wait4(pid_t upid, int __user *stat_addr,
+			int options, struct rusage *ru)
 {
 	struct wait_opts wo;
 	struct pid *pid = NULL;
@@ -1724,6 +1742,19 @@ SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
 	return ret;
 }
 
+SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
+		int, options, struct rusage __user *, ru)
+{
+	struct rusage r;
+	long err = kernel_wait4(upid, stat_addr, options, ru ? &r : NULL);
+
+	if (err > 0) {
+		if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
+			return -EFAULT;
+	}
+	return err;
+}
+
 #ifdef __ARCH_WANT_SYS_WAITPID
 
 /*
@@ -1744,29 +1775,13 @@ COMPAT_SYSCALL_DEFINE4(wait4,
 	int, options,
 	struct compat_rusage __user *, ru)
 {
-	if (!ru) {
-		return sys_wait4(pid, stat_addr, options, NULL);
-	} else {
 	struct rusage r;
-		int ret;
-		unsigned int status;
-		mm_segment_t old_fs = get_fs();
-
-		set_fs (KERNEL_DS);
-		ret = sys_wait4(pid,
-				(stat_addr ?
-				 (unsigned int __user *) &status : NULL),
-				options, (struct rusage __user *) &r);
-		set_fs (old_fs);
-
-		if (ret > 0) {
-			if (put_compat_rusage(&r, ru))
-				return -EFAULT;
-			if (stat_addr && put_user(status, stat_addr))
+	long err = kernel_wait4(pid, stat_addr, options, ru ? &r : NULL);
+	if (err > 0) {
+		if (ru && put_compat_rusage(&r, ru))
 			return -EFAULT;
 	}
-		return ret;
-	}
+	return err;
 }
 
 COMPAT_SYSCALL_DEFINE5(waitid,
@@ -1782,8 +1797,8 @@ COMPAT_SYSCALL_DEFINE5(waitid,
 	memset(&info, 0, sizeof(info));
 
 	set_fs(KERNEL_DS);
-	ret = sys_waitid(which, pid, (siginfo_t __user *)&info, options,
-			 uru ? (struct rusage __user *)&ru : NULL);
+	ret = kernel_waitid(which, pid, (siginfo_t __user *)&info, options,
+			 uru ? &ru : NULL);
 	set_fs(old_fs);
 
 	if ((ret < 0) || (info.si_signo == 0))

kernel/sys.c

@@ -1552,7 +1552,7 @@ static void accumulate_thread_rusage(struct task_struct *t, struct rusage *r)
 	r->ru_oublock += task_io_get_oublock(t);
 }
 
-static void k_getrusage(struct task_struct *p, int who, struct rusage *r)
+void getrusage(struct task_struct *p, int who, struct rusage *r)
 {
 	struct task_struct *t;
 	unsigned long flags;
@@ -1626,20 +1626,16 @@ static void k_getrusage(struct task_struct *p, int who, struct rusage *r)
 	r->ru_maxrss = maxrss * (PAGE_SIZE / 1024); /* convert pages to KBs */
 }
 
-int getrusage(struct task_struct *p, int who, struct rusage __user *ru)
+SYSCALL_DEFINE2(getrusage, int, who, struct rusage __user *, ru)
 {
 	struct rusage r;
 
-	k_getrusage(p, who, &r);
-	return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0;
-}
-
-SYSCALL_DEFINE2(getrusage, int, who, struct rusage __user *, ru)
-{
 	if (who != RUSAGE_SELF && who != RUSAGE_CHILDREN &&
 	    who != RUSAGE_THREAD)
 		return -EINVAL;
-	return getrusage(current, who, ru);
+
+	getrusage(current, who, &r);
+	return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0;
 }
 
 #ifdef CONFIG_COMPAT
@@ -1651,7 +1647,7 @@ COMPAT_SYSCALL_DEFINE2(getrusage, int, who, struct compat_rusage __user *, ru)
 	    who != RUSAGE_THREAD)
 		return -EINVAL;
 
-	k_getrusage(current, who, &r);
+	getrusage(current, who, &r);
 	return put_compat_rusage(&r, ru);
 }
 #endif