reiserfs: fix oops while creating privroot with selinux enabled

Commit 57fe60df ("reiserfs: add atomic addition of selinux attributes
during inode creation") contains a bug that will cause it to oops when
mounting a file system that didn't previously contain extended attributes
on a system using security.* xattrs.

The issue is that while creating the privroot during mount
reiserfs_security_init calls reiserfs_xattr_jcreate_nblocks which
dereferences the xattr root.  The xattr root doesn't exist, so we get an
oops.

Addresses http://bugzilla.kernel.org/show_bug.cgi?id=15309

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/reiserfs/xattr_security.c

@@ -76,7 +76,7 @@ int reiserfs_security_init(struct inode *dir, struct inode *inode,
 		return error;
 	}
 
-	if (sec->length) {
+	if (sec->length && reiserfs_xattrs_initialized(inode->i_sb)) {
 		blocks = reiserfs_xattr_jcreate_nblocks(inode) +
 			 reiserfs_xattr_nblocks(inode, sec->length);
 		/* We don't want to count the directories twice if we have

include/linux/reiserfs_xattr.h

@@ -70,6 +70,11 @@ int reiserfs_security_write(struct reiserfs_transaction_handle *th,
 void reiserfs_security_free(struct reiserfs_security_handle *sec);
 #endif
 
+static inline int reiserfs_xattrs_initialized(struct super_block *sb)
+{
+	return REISERFS_SB(sb)->priv_root != NULL;
+}
+
 #define xattr_size(size) ((size) + sizeof(struct reiserfs_xattr_header))
 static inline loff_t reiserfs_xattr_nblocks(struct inode *inode, loff_t size)
 {