Merge tag 'driver-core-3.15-rc6' of...

Merge tag 'driver-core-3.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core

Pull driver core fixes from Greg KH:
 "Here are two driver core (well, sysfs) fixes for 3.15-rc6 that resolve
  some reported issues and a regression from 3.13"

* tag 'driver-core-3.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core:
  sysfs: make sure read buffer is zeroed
  kernfs, sysfs, cgroup: restrict extra perm check on open to sysfs

fs/kernfs/file.c

@@ -610,6 +610,7 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
 static int kernfs_fop_open(struct inode *inode, struct file *file)
 {
 	struct kernfs_node *kn = file->f_path.dentry->d_fsdata;
+	struct kernfs_root *root = kernfs_root(kn);
 	const struct kernfs_ops *ops;
 	struct kernfs_open_file *of;
 	bool has_read, has_write, has_mmap;
@@ -624,7 +625,8 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
 	has_write = ops->write || ops->mmap;
 	has_mmap = ops->mmap;
 
-	/* check perms and supported operations */
+	/* see the flag definition for details */
+	if (root->flags & KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK) {
 		if ((file->f_mode & FMODE_WRITE) &&
 		    (!(inode->i_mode & S_IWUGO) || !has_write))
 			goto err_out;
@@ -632,6 +634,7 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
 		if ((file->f_mode & FMODE_READ) &&
 		    (!(inode->i_mode & S_IRUGO) || !has_read))
 			goto err_out;
+	}
 
 	/* allocate a kernfs_open_file for the file */
 	error = -ENOMEM;

fs/sysfs/file.c

@@ -47,12 +47,13 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
 	ssize_t count;
 	char *buf;
 
-	/* acquire buffer and ensure that it's >= PAGE_SIZE */
+	/* acquire buffer and ensure that it's >= PAGE_SIZE and clear */
 	count = seq_get_buf(sf, &buf);
 	if (count < PAGE_SIZE) {
 		seq_commit(sf, -1);
 		return 0;
 	}
+	memset(buf, 0, PAGE_SIZE);
 
 	/*
 	 * Invoke show().  Control may reach here via seq file lseek even

fs/sysfs/mount.c

@@ -63,7 +63,8 @@ int __init sysfs_init(void)
 {
 	int err;
 
-	sysfs_root = kernfs_create_root(NULL, 0, NULL);
+	sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
+					NULL);
 	if (IS_ERR(sysfs_root))
 		return PTR_ERR(sysfs_root);
 

include/linux/kernfs.h

@@ -50,7 +50,24 @@ enum kernfs_node_flag {
 
 /* @flags for kernfs_create_root() */
 enum kernfs_root_flag {
+	/*
+	 * kernfs_nodes are created in the deactivated state and invisible.
+	 * They require explicit kernfs_activate() to become visible.  This
+	 * can be used to make related nodes become visible atomically
+	 * after all nodes are created successfully.
+	 */
 	KERNFS_ROOT_CREATE_DEACTIVATED		= 0x0001,
+
+	/*
+	 * For regular flies, if the opener has CAP_DAC_OVERRIDE, open(2)
+	 * succeeds regardless of the RW permissions.  sysfs had an extra
+	 * layer of enforcement where open(2) fails with -EACCES regardless
+	 * of CAP_DAC_OVERRIDE if the permission doesn't have the
+	 * respective read or write access at all (none of S_IRUGO or
+	 * S_IWUGO) or the respective operation isn't implemented.  The
+	 * following flag enables that behavior.
+	 */
+	KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK	= 0x0002,
 };
 
 /* type-specific structures for kernfs_node union members */