[PATCH 1/1] sys_setrlimit: make sure ->rlim_max never grows

[Oleg Nesterov <oleg@redhat.com>]

Mostly preparation for Jiri's changes, but probably makes sense anyway.

sys_setrlimit() checks new_rlim.rlim_max <= old_rlim->rlim_max, but when
it takes task_lock() old_rlim->rlim_max can be already lowered. Move this
check under task_lock().

Currently this is not important, we can only race with our sub-thread,
this means the application is stupid. But when we change the code to allow
the update of !current task's limits, it becomes important to make sure
->rlim_max can be lowered "reliably" even if we race with the application
doing sys_setrlimit().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

 kernel/sys.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

--- WAIT/kernel/sys.c~SETRLIMIT	2009-06-17 14:11:26.000000000 +0200
+++ WAIT/kernel/sys.c	2009-09-03 19:01:48.000000000 +0200
@@ -1247,10 +1247,6 @@ SYSCALL_DEFINE2(setrlimit, unsigned int,
 		return -EFAULT;
 	if (new_rlim.rlim_cur > new_rlim.rlim_max)
 		return -EINVAL;
-	old_rlim = current->signal->rlim + resource;
-	if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
-	    !capable(CAP_SYS_RESOURCE))
-		return -EPERM;
 	if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > sysctl_nr_open)
 		return -EPERM;
 
@@ -1268,13 +1264,17 @@ SYSCALL_DEFINE2(setrlimit, unsigned int,
 		new_rlim.rlim_cur = 1;
 	}
 
+	old_rlim = current->signal->rlim + resource;
 	task_lock(current->group_leader);
-	*old_rlim = new_rlim;
+	if ((new_rlim.rlim_max <= old_rlim->rlim_max) ||
+				capable(CAP_SYS_RESOURCE))
+		*old_rlim = new_rlim;
+	else
+		retval = -EPERM;
 	task_unlock(current->group_leader);
 
-	if (resource != RLIMIT_CPU)
+	if (retval || resource != RLIMIT_CPU)
 		goto out;
-
 	/*
 	 * RLIMIT_CPU handling.   Note that the kernel fails to return an error
 	 * code if it rejected the user's attempt to set RLIMIT_CPU.  This is a
@@ -1286,7 +1286,7 @@ SYSCALL_DEFINE2(setrlimit, unsigned int,
 
 	update_rlimit_cpu(new_rlim.rlim_cur);
 out:
-	return 0;
+	return retval;
 }
 
 /*