[RFC/PATCH 7/8]: CGroup Files: Convert devcgroup_access_write() into a cgroup write_string() handler

[menage]

This patch converts devcgroup_access_write() from a raw file handler
into a handler for the cgroup write_string() method. This allows some
boilerplate copying/locking/checking to be removed and simplifies the
cleanup path, since these functions are performed by the cgroups
framework before calling the handler.

Signed-off-by: Paul Menage <menage@xxxxxxxxxx>

---
 security/device_cgroup.c |   79 +++++++++++++----------------------------------
 1 file changed, 22 insertions(+), 57 deletions(-)

Index: cgroup-2.6.25-mm1/security/device_cgroup.c
===================================================================
--- cgroup-2.6.25-mm1.orig/security/device_cgroup.c
+++ cgroup-2.6.25-mm1/security/device_cgroup.c
@@ -323,14 +323,14 @@ static int parent_has_perm(struct cgroup
  * new access is only allowed if you're in the top-level cgroup, or your
  * parent cgroup has the access you're asking for.
  */
-static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
-				struct file *file, const char __user *userbuf,
-				size_t nbytes, loff_t *ppos)
+static int devcgroup_access_write(struct cgroup *cgroup,
+				  struct cftype *cft,
+				  char *buffer)
 {
 	struct cgroup *cur_cgroup;
 	struct dev_cgroup *devcgroup, *cur_devcgroup;
 	int filetype = cft->private;
-	char *buffer, *b;
+	char *b;
 	int retval = 0, count;
 	struct dev_whitelist_item wh;
 
@@ -341,22 +341,6 @@ static ssize_t devcgroup_access_write(st
 	cur_cgroup = task_cgroup(current, devices_subsys.subsys_id);
 	cur_devcgroup = cgroup_to_devcgroup(cur_cgroup);
 
-	buffer = kmalloc(nbytes+1, GFP_KERNEL);
-	if (!buffer)
-		return -ENOMEM;
-
-	if (copy_from_user(buffer, userbuf, nbytes)) {
-		retval = -EFAULT;
-		goto out1;
-	}
-	buffer[nbytes] = 0;	/* nul-terminate */
-
-	cgroup_lock();
-	if (cgroup_is_removed(cgroup)) {
-		retval = -ENODEV;
-		goto out2;
-	}
-
 	memset(&wh, 0, sizeof(wh));
 	b = buffer;
 
@@ -372,14 +356,11 @@ static ssize_t devcgroup_access_write(st
 		wh.type = DEV_CHAR;
 		break;
 	default:
-		retval = -EINVAL;
-		goto out2;
+		return -EINVAL;
 	}
 	b++;
-	if (!isspace(*b)) {
-		retval = -EINVAL;
-		goto out2;
-	}
+	if (!isspace(*b))
+		return -EINVAL;
 	b++;
 	if (*b == '*') {
 		wh.major = ~0;
@@ -391,13 +372,10 @@ static ssize_t devcgroup_access_write(st
 			b++;
 		}
 	} else {
-		retval = -EINVAL;
-		goto out2;
-	}
-	if (*b != ':') {
-		retval = -EINVAL;
-		goto out2;
+		return -EINVAL;
 	}
+	if (*b != ':')
+		return -EINVAL;
 	b++;
 
 	/* read minor */
@@ -411,13 +389,10 @@ static ssize_t devcgroup_access_write(st
 			b++;
 		}
 	} else {
-		retval = -EINVAL;
-		goto out2;
-	}
-	if (!isspace(*b)) {
-		retval = -EINVAL;
-		goto out2;
+		return -EINVAL;
 	}
+	if (!isspace(*b))
+		return -EINVAL;
 	for (b++, count = 0; count < 3; count++, b++) {
 		switch (*b) {
 		case 'r':
@@ -434,8 +409,7 @@ static ssize_t devcgroup_access_write(st
 			count = 3;
 			break;
 		default:
-			retval = -EINVAL;
-			goto out2;
+			return -EINVAL;
 		}
 	}
 
@@ -444,38 +418,29 @@ handle:
 	switch (filetype) {
 	case DEVCG_ALLOW:
 		if (!parent_has_perm(cgroup, &wh))
-			retval = -EPERM;
-		else
-			retval = dev_whitelist_add(devcgroup, &wh);
-		break;
+			return -EPERM;
+		return dev_whitelist_add(devcgroup, &wh);
 	case DEVCG_DENY:
 		dev_whitelist_rm(devcgroup, &wh);
 		break;
 	default:
-		retval = -EINVAL;
-		goto out2;
+		return -EINVAL;
 	}
-
-	if (retval == 0)
-		retval = nbytes;
-
-out2:
-	cgroup_unlock();
-out1:
-	kfree(buffer);
-	return retval;
+	return 0;
 }
 
 static struct cftype dev_cgroup_files[] = {
 	{
 		.name = "allow",
-		.write  = devcgroup_access_write,
+		.write_string  = devcgroup_access_write,
 		.private = DEVCG_ALLOW,
+		.lockmode = CFT_LOCK_CGL_WRITE,
 	},
 	{
 		.name = "deny",
-		.write = devcgroup_access_write,
+		.write_string = devcgroup_access_write,
 		.private = DEVCG_DENY,
+		.lockmode = CFT_LOCK_CGL_WRITE,
 	},
 	{
 		.name = "list",

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