[PATCH] Generic VFS fallback for security xattrs

This patch modifies the VFS setxattr, getxattr, and listxattr code to fall
back to the security module for security xattrs if the filesystem does not
support xattrs natively.  This allows security modules to export the incore
inode security label information to userspace even if the filesystem does
not provide xattr storage, and eliminates the need to individually patch
various pseudo filesystem types to provide such access.  The patch removes
the existing xattr code from devpts and tmpfs as it is then no longer
needed.

The patch restructures the code flow slightly to reduce duplication between
the normal path and the fallback path, but this should only have one
user-visible side effect - a program may get -EACCES rather than
-EOPNOTSUPP if policy denied access but the filesystem didn't support the
operation anyway.  Note that the post_setxattr hook call is not needed in
the fallback case, as the inode_setsecurity hook call handles the incore
inode security state update directly.  In contrast, we do call fsnotify in
both cases.
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/Kconfig

@@ -783,28 +783,6 @@ config SYSFS
 
 	Designers of embedded systems may wish to say N here to conserve space.
 
-config DEVPTS_FS_XATTR
-	bool "/dev/pts Extended Attributes"
-	depends on UNIX98_PTYS
-	help
-	  Extended attributes are name:value pairs associated with inodes by
-	  the kernel or by users (see the attr(5) manual page, or visit
-	  <http://acl.bestbits.at/> for details).
-
-	  If unsure, say N.
-
-config DEVPTS_FS_SECURITY
-	bool "/dev/pts Security Labels"
-	depends on DEVPTS_FS_XATTR
-	help
-	  Security labels support alternative access control models
-	  implemented by security modules like SELinux.  This option
-	  enables an extended attribute handler for file security
-	  labels in the /dev/pts filesystem.
-
-	  If you are not using a security module that requires using
-	  extended attributes for file security labels, say N.
-
 config TMPFS
 	bool "Virtual memory file system support (former shm fs)"
 	help
@@ -817,27 +795,6 @@ config TMPFS
 
 	  See <file:Documentation/filesystems/tmpfs.txt> for details.
 
-config TMPFS_XATTR
-	bool "tmpfs Extended Attributes"
-	depends on TMPFS
-	help
-	  Extended attributes are name:value pairs associated with inodes by
-	  the kernel or by users (see the attr(5) manual page, or visit
-	  <http://acl.bestbits.at/> for details).
-
-	  If unsure, say N.
-
-config TMPFS_SECURITY
-	bool "tmpfs Security Labels"
-	depends on TMPFS_XATTR
-	help
-	  Security labels support alternative access control models
-	  implemented by security modules like SELinux.  This option
-	  enables an extended attribute handler for file security
-	  labels in the tmpfs filesystem.
-	  If you are not using a security module that requires using
-	  extended attributes for file security labels, say N.
-
 config HUGETLBFS
 	bool "HugeTLB file system support"
 	depends X86 || IA64 || PPC64 || SPARC64 || SUPERH || X86_64 || BROKEN

fs/devpts/Makefile

@@ -5,4 +5,3 @@
 obj-$(CONFIG_UNIX98_PTYS)		+= devpts.o
 
 devpts-$(CONFIG_UNIX98_PTYS)		:= inode.o
-devpts-$(CONFIG_DEVPTS_FS_SECURITY)	+= xattr_security.o

fs/devpts/inode.c

@@ -18,28 +18,9 @@
 #include <linux/mount.h>
 #include <linux/tty.h>
 #include <linux/devpts_fs.h>
-#include <linux/xattr.h>
 
 #define DEVPTS_SUPER_MAGIC 0x1cd1
 
-extern struct xattr_handler devpts_xattr_security_handler;
-
-static struct xattr_handler *devpts_xattr_handlers[] = {
-#ifdef CONFIG_DEVPTS_FS_SECURITY
-	&devpts_xattr_security_handler,
-#endif
-	NULL
-};
-
-static struct inode_operations devpts_file_inode_operations = {
-#ifdef CONFIG_DEVPTS_FS_XATTR
-	.setxattr	= generic_setxattr,
-	.getxattr	= generic_getxattr,
-	.listxattr	= generic_listxattr,
-	.removexattr	= generic_removexattr,
-#endif
-};
-
 static struct vfsmount *devpts_mnt;
 static struct dentry *devpts_root;
 
@@ -102,7 +83,6 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
 	s->s_blocksize_bits = 10;
 	s->s_magic = DEVPTS_SUPER_MAGIC;
 	s->s_op = &devpts_sops;
-	s->s_xattr = devpts_xattr_handlers;
 	s->s_time_gran = 1;
 
 	inode = new_inode(s);
@@ -175,7 +155,6 @@ int devpts_pty_new(struct tty_struct *tty)
 	inode->i_gid = config.setgid ? config.gid : current->fsgid;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	init_special_inode(inode, S_IFCHR|config.mode, device);
-	inode->i_op = &devpts_file_inode_operations;
 	inode->u.generic_ip = tty;
 
 	dentry = get_node(number);

fs/devpts/xattr_security.c

-/*
- * Security xattr support for devpts.
- *
- * Author: Stephen Smalley <sds@epoch.ncsc.mil>
- * Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License as published by the Free
- * Software Foundation; either version 2 of the License, or (at your option)
- * any later version.
- */
-#include <linux/string.h>
-#include <linux/fs.h>
-#include <linux/security.h>
-#include <linux/xattr.h>
-
-static size_t
-devpts_xattr_security_list(struct inode *inode, char *list, size_t list_len,
-			   const char *name, size_t name_len)
-{
-	return security_inode_listsecurity(inode, list, list_len);
-}
-
-static int
-devpts_xattr_security_get(struct inode *inode, const char *name,
-			  void *buffer, size_t size)
-{
-	if (strcmp(name, "") == 0)
-		return -EINVAL;
-	return security_inode_getsecurity(inode, name, buffer, size);
-}
-
-static int
-devpts_xattr_security_set(struct inode *inode, const char *name,
-			  const void *value, size_t size, int flags)
-{
-	if (strcmp(name, "") == 0)
-		return -EINVAL;
-	return security_inode_setsecurity(inode, name, value, size, flags);
-}
-
-struct xattr_handler devpts_xattr_security_handler = {
-	.prefix	= XATTR_SECURITY_PREFIX,
-	.list	= devpts_xattr_security_list,
-	.get	= devpts_xattr_security_get,
-	.set	= devpts_xattr_security_set,
-};

fs/xattr.c

@@ -51,20 +51,29 @@ setxattr(struct dentry *d, char __user *name, void __user *value,
 		}
 	}
 
-	error = -EOPNOTSUPP;
-	if (d->d_inode->i_op && d->d_inode->i_op->setxattr) {
 	down(&d->d_inode->i_sem);
 	error = security_inode_setxattr(d, kname, kvalue, size, flags);
 	if (error)
 		goto out;
-		error = d->d_inode->i_op->setxattr(d, kname, kvalue, size, flags);
+	error = -EOPNOTSUPP;
+	if (d->d_inode->i_op && d->d_inode->i_op->setxattr) {
+		error = d->d_inode->i_op->setxattr(d, kname, kvalue,
+						   size, flags);
 		if (!error) {
 			fsnotify_xattr(d);
-			security_inode_post_setxattr(d, kname, kvalue, size, flags);
+			security_inode_post_setxattr(d, kname, kvalue,
+						     size, flags);
+		}
+	} else if (!strncmp(kname, XATTR_SECURITY_PREFIX,
+			    sizeof XATTR_SECURITY_PREFIX - 1)) {
+		const char *suffix = kname + sizeof XATTR_SECURITY_PREFIX - 1;
+		error = security_inode_setsecurity(d->d_inode, suffix, kvalue,
+						   size, flags);
+		if (!error)
+			fsnotify_xattr(d);
 	}
 out:
 	up(&d->d_inode->i_sem);
-	}
 	if (kvalue)
 		kfree(kvalue);
 	return error;
@@ -139,12 +148,18 @@ getxattr(struct dentry *d, char __user *name, void __user *value, size_t size)
 			return -ENOMEM;
 	}
 
-	error = -EOPNOTSUPP;
-	if (d->d_inode->i_op && d->d_inode->i_op->getxattr) {
 	error = security_inode_getxattr(d, kname);
 	if (error)
 		goto out;
+	error = -EOPNOTSUPP;
+	if (d->d_inode->i_op && d->d_inode->i_op->getxattr)
 		error = d->d_inode->i_op->getxattr(d, kname, kvalue, size);
+	else if (!strncmp(kname, XATTR_SECURITY_PREFIX,
+			  sizeof XATTR_SECURITY_PREFIX - 1)) {
+		const char *suffix = kname + sizeof XATTR_SECURITY_PREFIX - 1;
+		error = security_inode_getsecurity(d->d_inode, suffix, kvalue,
+						   size);
+	}
 	if (error > 0) {
 		if (size && copy_to_user(value, kvalue, error))
 			error = -EFAULT;
@@ -153,7 +168,6 @@ getxattr(struct dentry *d, char __user *name, void __user *value, size_t size)
 		   than XATTR_SIZE_MAX bytes. Not possible. */
 		error = -E2BIG;
 	}
-	}
 out:
 	if (kvalue)
 		kfree(kvalue);
@@ -221,12 +235,17 @@ listxattr(struct dentry *d, char __user *list, size_t size)
 			return -ENOMEM;
 	}
 
-	error = -EOPNOTSUPP;
-	if (d->d_inode->i_op && d->d_inode->i_op->listxattr) {
 	error = security_inode_listxattr(d);
 	if (error)
 		goto out;
+	error = -EOPNOTSUPP;
+	if (d->d_inode->i_op && d->d_inode->i_op->listxattr) {
 		error = d->d_inode->i_op->listxattr(d, klist, size);
+	} else {
+		error = security_inode_listsecurity(d->d_inode, klist, size);
+		if (size && error >= size)
+			error = -ERANGE;
+	}
 	if (error > 0) {
 		if (size && copy_to_user(list, klist, error))
 			error = -EFAULT;
@@ -235,7 +254,6 @@ listxattr(struct dentry *d, char __user *list, size_t size)
 		   than XATTR_LIST_MAX bytes. Not possible. */
 		error = -E2BIG;
 	}
-	}
 out:
 	if (klist)
 		kfree(klist);

mm/shmem.c

@@ -45,7 +45,6 @@
 #include <linux/swapops.h>
 #include <linux/mempolicy.h>
 #include <linux/namei.h>
-#include <linux/xattr.h>
 #include <asm/uaccess.h>
 #include <asm/div64.h>
 #include <asm/pgtable.h>
@@ -179,7 +178,6 @@ static struct address_space_operations shmem_aops;
 static struct file_operations shmem_file_operations;
 static struct inode_operations shmem_inode_operations;
 static struct inode_operations shmem_dir_inode_operations;
-static struct inode_operations shmem_special_inode_operations;
 static struct vm_operations_struct shmem_vm_ops;
 
 static struct backing_dev_info shmem_backing_dev_info = {
@@ -1300,7 +1298,6 @@ shmem_get_inode(struct super_block *sb, int mode, dev_t dev)
 
 		switch (mode & S_IFMT) {
 		default:
-			inode->i_op = &shmem_special_inode_operations;
 			init_special_inode(inode, mode, dev);
 			break;
 		case S_IFREG:
@@ -1804,12 +1801,6 @@ static void shmem_put_link(struct dentry *dentry, struct nameidata *nd, void *co
 static struct inode_operations shmem_symlink_inline_operations = {
 	.readlink	= generic_readlink,
 	.follow_link	= shmem_follow_link_inline,
-#ifdef CONFIG_TMPFS_XATTR
-	.setxattr       = generic_setxattr,
-	.getxattr       = generic_getxattr,
-	.listxattr      = generic_listxattr,
-	.removexattr    = generic_removexattr,
-#endif
 };
 
 static struct inode_operations shmem_symlink_inode_operations = {
@@ -1817,12 +1808,6 @@ static struct inode_operations shmem_symlink_inode_operations = {
 	.readlink	= generic_readlink,
 	.follow_link	= shmem_follow_link,
 	.put_link	= shmem_put_link,
-#ifdef CONFIG_TMPFS_XATTR
-	.setxattr       = generic_setxattr,
-	.getxattr       = generic_getxattr,
-	.listxattr      = generic_listxattr,
-	.removexattr    = generic_removexattr,
-#endif
 };
 
 static int shmem_parse_options(char *options, int *mode, uid_t *uid, gid_t *gid, unsigned long *blocks, unsigned long *inodes)
@@ -1942,12 +1927,6 @@ static void shmem_put_super(struct super_block *sb)
 	sb->s_fs_info = NULL;
 }
 
-#ifdef CONFIG_TMPFS_XATTR
-static struct xattr_handler *shmem_xattr_handlers[];
-#else
-#define shmem_xattr_handlers NULL
-#endif
-
 static int shmem_fill_super(struct super_block *sb,
 			    void *data, int silent)
 {
@@ -1998,7 +1977,6 @@ static int shmem_fill_super(struct super_block *sb,
 	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
 	sb->s_magic = TMPFS_MAGIC;
 	sb->s_op = &shmem_ops;
-	sb->s_xattr = shmem_xattr_handlers;
 
 	inode = shmem_get_inode(sb, S_IFDIR | mode, 0);
 	if (!inode)
@@ -2087,12 +2065,6 @@ static struct file_operations shmem_file_operations = {
 static struct inode_operations shmem_inode_operations = {
 	.truncate	= shmem_truncate,
 	.setattr	= shmem_notify_change,
-#ifdef CONFIG_TMPFS_XATTR
-	.setxattr       = generic_setxattr,
-	.getxattr       = generic_getxattr,
-	.listxattr      = generic_listxattr,
-	.removexattr    = generic_removexattr,
-#endif
 };
 
 static struct inode_operations shmem_dir_inode_operations = {
@@ -2106,21 +2078,6 @@ static struct inode_operations shmem_dir_inode_operations = {
 	.rmdir		= shmem_rmdir,
 	.mknod		= shmem_mknod,
 	.rename		= shmem_rename,
-#ifdef CONFIG_TMPFS_XATTR
-	.setxattr       = generic_setxattr,
-	.getxattr       = generic_getxattr,
-	.listxattr      = generic_listxattr,
-	.removexattr    = generic_removexattr,
-#endif
-#endif
-};
-
-static struct inode_operations shmem_special_inode_operations = {
-#ifdef CONFIG_TMPFS_XATTR
-	.setxattr	= generic_setxattr,
-	.getxattr	= generic_getxattr,
-	.listxattr	= generic_listxattr,
-	.removexattr	= generic_removexattr,
 #endif
 };
 
@@ -2146,48 +2103,6 @@ static struct vm_operations_struct shmem_vm_ops = {
 };
 
 
-#ifdef CONFIG_TMPFS_SECURITY
-
-static size_t shmem_xattr_security_list(struct inode *inode, char *list, size_t list_len,
-					const char *name, size_t name_len)
-{
-	return security_inode_listsecurity(inode, list, list_len);
-}
-
-static int shmem_xattr_security_get(struct inode *inode, const char *name, void *buffer, size_t size)
-{
-	if (strcmp(name, "") == 0)
-		return -EINVAL;
-	return security_inode_getsecurity(inode, name, buffer, size);
-}
-
-static int shmem_xattr_security_set(struct inode *inode, const char *name, const void *value, size_t size, int flags)
-{
-	if (strcmp(name, "") == 0)
-		return -EINVAL;
-	return security_inode_setsecurity(inode, name, value, size, flags);
-}
-
-static struct xattr_handler shmem_xattr_security_handler = {
-	.prefix	= XATTR_SECURITY_PREFIX,
-	.list	= shmem_xattr_security_list,
-	.get	= shmem_xattr_security_get,
-	.set	= shmem_xattr_security_set,
-};
-
-#endif	/* CONFIG_TMPFS_SECURITY */
-
-#ifdef CONFIG_TMPFS_XATTR
-
-static struct xattr_handler *shmem_xattr_handlers[] = {
-#ifdef CONFIG_TMPFS_SECURITY
-	&shmem_xattr_security_handler,
-#endif
-	NULL
-};
-
-#endif	/* CONFIG_TMPFS_XATTR */
-
 static struct super_block *shmem_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {