[PATCH v14 0/4] SELinux support for anonymous inodes and UFFD

[PATCH v14 0/4] SELinux support for anonymous inodes and UFFD

[Lokesh Gidra]

Userfaultfd in unprivileged contexts could be potentially very
useful. We'd like to harden userfaultfd to make such unprivileged use
less risky. This patch series allows SELinux to manage userfaultfd
file descriptors and in the future, other kinds of
anonymous-inode-based file descriptor.  SELinux policy authors can
apply policy types to anonymous inodes by providing name-based
transition rules keyed off the anonymous inode internal name (
"[userfaultfd]" in the case of userfaultfd(2) file descriptors) and
applying policy to the new SIDs thus produced.

With SELinux managed userfaultfd, an admin can control creation and
movement of the file descriptors. In particular, handling of
a userfaultfd descriptor by a different process is essentially a
ptrace access into the process, without any of the corresponding
security_ptrace_access_check() checks. For privacy, the admin may
want to deny such accesses, which is possible with SELinux support.

Inside the kernel, a new anon_inode interface, anon_inode_getfd_secure,
allows callers to opt into this SELinux management. In this new "secure"
mode, anon_inodes create new ephemeral inodes for anonymous file objects
instead of reusing the normal anon_inodes singleton dummy inode. A new
LSM hook gives security modules an opportunity to configure and veto
these ephemeral inodes.

This patch series is one of two fork of [1] and is an
alternative to [2].

The primary difference between the two patch series is that this
partch series creates a unique inode for each "secure" anonymous
inode, while the other patch series ([2]) continues using the
singleton dummy anonymous inode and adds a way to attach SELinux
security information directly to file objects.

I prefer the approach in this patch series because 1) it's a smaller
patch than [2], and 2) it produces a more regular security
architecture: in this patch series, secure anonymous inodes aren't
S_PRIVATE and they maintain the SELinux property that the label for a
file is in its inode. We do need an additional inode per anonymous
file, but per-struct-file inode creation doesn't seem to be a problem
for pipes and sockets.

The previous version of this feature ([1]) created a new SELinux
security class for userfaultfd file descriptors. This version adopts
the generic transition-based approach of [2].

This patch series also differs from [2] in that it doesn't affect all
anonymous inodes right away --- instead requiring anon_inodes callers
to opt in --- but this difference isn't one of basic approach. The
important question to resolve is whether we should be creating new
inodes or enhancing per-file data.

Changes from the first version of the patch:

  - Removed some error checks
  - Defined a new anon_inode SELinux class to resolve the
    ambiguity in [3]
  - Inherit sclass as well as descriptor from context inode

Changes from the second version of the patch:

  - Fixed example policy in the commit message to reflect the use of
    the new anon_inode class.

Changes from the third version of the patch:

  - Dropped the fops parameter to the LSM hook
  - Documented hook parameters
  - Fixed incorrect class used for SELinux transition
  - Removed stray UFFD changed early in the series
  - Removed a redundant ERR_PTR(PTR_ERR())

Changes from the fourth version of the patch:

  - Removed an unused parameter from an internal function
  - Fixed function documentation

Changes from the fifth version of the patch:

  - Fixed function documentation in fs/anon_inodes.c and
    include/linux/lsm_hooks.h
  - Used anon_inode_getfd_secure() in userfaultfd() syscall and removed
    owner from userfaultfd_ctx.

Changes from the sixth version of the patch:

  - Removed definition of anon_inode_getfile_secure() as there are no
    callers.
  - Simplified function description of anon_inode_getfd_secure().
  - Elaborated more on the purpose of 'context_inode' in commit message.

Changes from the seventh version of the patch:

  - Fixed error handling in _anon_inode_getfile().
  - Fixed minor comment and indentation related issues.

Changes from the eighth version of the patch:

  - Replaced selinux_state.initialized with selinux_state.initialized

Changes from the ninth version of the patch:

  - Fixed function names in fs/anon_inodes.c
  - Fixed comment of anon_inode_getfd_secure()
  - Fixed name of the patch wherein userfaultfd code uses
    anon_inode_getfd_secure()

Changes from the tenth version of the patch:

  - Split first patch into VFS and LSM specific patches
  - Fixed comments in fs/anon_inodes.c
  - Fixed comment of alloc_anon_inode()

Changes from the eleventh version of the patch:

  - Removed comment of alloc_anon_inode() for consistency with the code
  - Fixed explanation of LSM hook in the commit message

Changes from the twelfth version of the patch:
  - Replaced FILE__CREATE with ANON_INODE__CREATE while initializing
    anon-inode's SELinux security struct.
  - Check context_inode's SELinux label and return -EACCES if it's
    invalid.

Changes from the thirteenth version of the patch:
  - Initialize anon-inode's sclass with SECCLASS_ANON_INODE.
  - Check if context_inode has sclass set to SECCLASS_ANON_INODE.

[1] https://lore.kernel.org/lkml/20200211225547.235083-1-dancol@google.com/
[2] https://lore.kernel.org/linux-fsdevel/20200213194157.5877-1-sds@tycho.nsa.gov/
[3] https://lore.kernel.org/lkml/23f725ca-5b5a-5938-fcc8-5bbbfc9ba9bc@tycho.nsa.gov/

Daniel Colascione (3):
  fs: add LSM-supporting anon-inode interface
  selinux: teach SELinux about anonymous inodes
  userfaultfd: use secure anon inodes for userfaultfd

Lokesh Gidra (1):
  security: add inode_init_security_anon() LSM hook

 fs/anon_inodes.c                    | 150 ++++++++++++++++++++--------
 fs/libfs.c                          |   5 -
 fs/userfaultfd.c                    |  19 ++--
 include/linux/anon_inodes.h         |   5 +
 include/linux/lsm_hook_defs.h       |   2 +
 include/linux/lsm_hooks.h           |   9 ++
 include/linux/security.h            |  10 ++
 security/security.c                 |   8 ++
 security/selinux/hooks.c            |  59 +++++++++++
 security/selinux/include/classmap.h |   2 +
 10 files changed, 215 insertions(+), 54 deletions(-)

-- 
2.30.0.284.gd98b1dd5eaa7-goog

[PATCH v14 1/4] security: add inode_init_security_anon() LSM hook

[Lokesh Gidra]

This change adds a new LSM hook, inode_init_security_anon(), that will
be used while creating secure anonymous inodes. The hook allows/denies
its creation and assigns a security context to the inode.

The new hook accepts an optional context_inode parameter that callers
can use to provide additional contextual information to security modules
for granting/denying permission to create an anon-inode of the same type.
This context_inode's security_context can also be used to initialize the
newly created anon-inode's security_context.

Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
---
 include/linux/lsm_hook_defs.h |  2 ++
 include/linux/lsm_hooks.h     |  9 +++++++++
 include/linux/security.h      | 10 ++++++++++
 security/security.c           |  8 ++++++++
 4 files changed, 29 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 7aaa753b8608..dfd261dcbcb0 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -113,6 +113,8 @@ LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode)
 LSM_HOOK(int, 0, inode_init_security, struct inode *inode,
 	 struct inode *dir, const struct qstr *qstr, const char **name,
 	 void **value, size_t *len)
+LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,
+	 const struct qstr *name, const struct inode *context_inode)
 LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry,
 	 umode_t mode)
 LSM_HOOK(int, 0, inode_link, struct dentry *old_dentry, struct inode *dir,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index a19adef1f088..bdfc8a76a4f7 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -233,6 +233,15 @@
  *	Returns 0 if @name and @value have been successfully set,
  *	-EOPNOTSUPP if no security attribute is needed, or
  *	-ENOMEM on memory allocation failure.
+ * @inode_init_security_anon:
+ *      Set up the incore security field for the new anonymous inode
+ *      and return whether the inode creation is permitted by the security
+ *      module or not.
+ *      @inode contains the inode structure
+ *      @name name of the anonymous inode class
+ *      @context_inode optional related inode
+ *	Returns 0 on success, -EACCES if the security module denies the
+ *	creation of this inode, or another -errno upon other errors.
  * @inode_create:
  *	Check permission to create a regular file.
  *	@dir contains inode structure of the parent of the new file.
diff --git a/include/linux/security.h b/include/linux/security.h
index c35ea0ffccd9..b0d14f04b16d 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -324,6 +324,9 @@ void security_inode_free(struct inode *inode);
 int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const struct qstr *qstr,
 				 initxattrs initxattrs, void *fs_data);
+int security_inode_init_security_anon(struct inode *inode,
+				      const struct qstr *name,
+				      const struct inode *context_inode);
 int security_old_inode_init_security(struct inode *inode, struct inode *dir,
 				     const struct qstr *qstr, const char **name,
 				     void **value, size_t *len);
@@ -738,6 +741,13 @@ static inline int security_inode_init_security(struct inode *inode,
 	return 0;
 }
 
+static inline int security_inode_init_security_anon(struct inode *inode,
+						    const struct qstr *name,
+						    const struct inode *context_inode)
+{
+	return 0;
+}
+
 static inline int security_old_inode_init_security(struct inode *inode,
 						   struct inode *dir,
 						   const struct qstr *qstr,
diff --git a/security/security.c b/security/security.c
index 7b09cfbae94f..401663b5b70e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1059,6 +1059,14 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 }
 EXPORT_SYMBOL(security_inode_init_security);
 
+int security_inode_init_security_anon(struct inode *inode,
+				      const struct qstr *name,
+				      const struct inode *context_inode)
+{
+	return call_int_hook(inode_init_security_anon, 0, inode, name,
+			     context_inode);
+}
+
 int security_old_inode_init_security(struct inode *inode, struct inode *dir,
 				     const struct qstr *qstr, const char **name,
 				     void **value, size_t *len)
-- 
2.30.0.284.gd98b1dd5eaa7-goog

[PATCH v14 2/4] fs: add LSM-supporting anon-inode interface

[Lokesh Gidra]

From: Daniel Colascione <dancol@google.com>

This change adds a new function, anon_inode_getfd_secure, that creates
anonymous-node file with individual non-S_PRIVATE inode to which security
modules can apply policy. Existing callers continue using the original
singleton-inode kind of anonymous-inode file. We can transition anonymous
inode users to the new kind of anonymous inode in individual patches for
the sake of bisection and review.

The new function accepts an optional context_inode parameter that callers
can use to provide additional contextual information to security modules.
For example, in case of userfaultfd, the created inode is a 'logical child'
of the context_inode (userfaultfd inode of the parent process) in the sense
that it provides the security context required during creation of the child
process' userfaultfd inode.

Signed-off-by: Daniel Colascione <dancol@google.com>

[LG: Delete obsolete comments to alloc_anon_inode()]
[LG: Add context_inode description in comments to anon_inode_getfd_secure()]
[LG: Remove definition of anon_inode_getfile_secure() as there are no callers]
[LG: Make __anon_inode_getfile() static]
[LG: Use correct error cast in __anon_inode_getfile()]
[LG: Fix error handling in __anon_inode_getfile()]

Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
---
 fs/anon_inodes.c            | 150 ++++++++++++++++++++++++++----------
 fs/libfs.c                  |   5 --
 include/linux/anon_inodes.h |   5 ++
 3 files changed, 115 insertions(+), 45 deletions(-)

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 89714308c25b..023337d65a03 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -55,61 +55,79 @@ static struct file_system_type anon_inode_fs_type = {
 	.kill_sb	= kill_anon_super,
 };
 
-/**
- * anon_inode_getfile - creates a new file instance by hooking it up to an
- *                      anonymous inode, and a dentry that describe the "class"
- *                      of the file
- *
- * @name:    [in]    name of the "class" of the new file
- * @fops:    [in]    file operations for the new file
- * @priv:    [in]    private data for the new file (will be file's private_data)
- * @flags:   [in]    flags
- *
- * Creates a new file by hooking it on a single inode. This is useful for files
- * that do not need to have a full-fledged inode in order to operate correctly.
- * All the files created with anon_inode_getfile() will share a single inode,
- * hence saving memory and avoiding code duplication for the file/inode/dentry
- * setup.  Returns the newly created file* or an error pointer.
- */
-struct file *anon_inode_getfile(const char *name,
-				const struct file_operations *fops,
-				void *priv, int flags)
+static struct inode *anon_inode_make_secure_inode(
+	const char *name,
+	const struct inode *context_inode)
 {
-	struct file *file;
+	struct inode *inode;
+	const struct qstr qname = QSTR_INIT(name, strlen(name));
+	int error;
+
+	inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
+	if (IS_ERR(inode))
+		return inode;
+	inode->i_flags &= ~S_PRIVATE;
+	error =	security_inode_init_security_anon(inode, &qname, context_inode);
+	if (error) {
+		iput(inode);
+		return ERR_PTR(error);
+	}
+	return inode;
+}
 
-	if (IS_ERR(anon_inode_inode))
-		return ERR_PTR(-ENODEV);
+static struct file *__anon_inode_getfile(const char *name,
+					 const struct file_operations *fops,
+					 void *priv, int flags,
+					 const struct inode *context_inode,
+					 bool secure)
+{
+	struct inode *inode;
+	struct file *file;
 
 	if (fops->owner && !try_module_get(fops->owner))
 		return ERR_PTR(-ENOENT);
 
-	/*
-	 * We know the anon_inode inode count is always greater than zero,
-	 * so ihold() is safe.
-	 */
-	ihold(anon_inode_inode);
-	file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name,
+	if (secure) {
+		inode =	anon_inode_make_secure_inode(name, context_inode);
+		if (IS_ERR(inode)) {
+			file = ERR_CAST(inode);
+			goto err;
+		}
+	} else {
+		inode =	anon_inode_inode;
+		if (IS_ERR(inode)) {
+			file = ERR_PTR(-ENODEV);
+			goto err;
+		}
+		/*
+		 * We know the anon_inode inode count is always
+		 * greater than zero, so ihold() is safe.
+		 */
+		ihold(inode);
+	}
+
+	file = alloc_file_pseudo(inode, anon_inode_mnt, name,
 				 flags & (O_ACCMODE | O_NONBLOCK), fops);
 	if (IS_ERR(file))
-		goto err;
+		goto err_iput;
 
-	file->f_mapping = anon_inode_inode->i_mapping;
+	file->f_mapping = inode->i_mapping;
 
 	file->private_data = priv;
 
 	return file;
 
+err_iput:
+	iput(inode);
 err:
-	iput(anon_inode_inode);
 	module_put(fops->owner);
 	return file;
 }
-EXPORT_SYMBOL_GPL(anon_inode_getfile);
 
 /**
- * anon_inode_getfd - creates a new file instance by hooking it up to an
- *                    anonymous inode, and a dentry that describe the "class"
- *                    of the file
+ * anon_inode_getfile - creates a new file instance by hooking it up to an
+ *                      anonymous inode, and a dentry that describe the "class"
+ *                      of the file
  *
  * @name:    [in]    name of the "class" of the new file
  * @fops:    [in]    file operations for the new file
@@ -118,12 +136,23 @@ EXPORT_SYMBOL_GPL(anon_inode_getfile);
  *
  * Creates a new file by hooking it on a single inode. This is useful for files
  * that do not need to have a full-fledged inode in order to operate correctly.
- * All the files created with anon_inode_getfd() will share a single inode,
+ * All the files created with anon_inode_getfile() will share a single inode,
  * hence saving memory and avoiding code duplication for the file/inode/dentry
- * setup.  Returns new descriptor or an error code.
+ * setup.  Returns the newly created file* or an error pointer.
  */
-int anon_inode_getfd(const char *name, const struct file_operations *fops,
-		     void *priv, int flags)
+struct file *anon_inode_getfile(const char *name,
+				const struct file_operations *fops,
+				void *priv, int flags)
+{
+	return __anon_inode_getfile(name, fops, priv, flags, NULL, false);
+}
+EXPORT_SYMBOL_GPL(anon_inode_getfile);
+
+static int __anon_inode_getfd(const char *name,
+			      const struct file_operations *fops,
+			      void *priv, int flags,
+			      const struct inode *context_inode,
+			      bool secure)
 {
 	int error, fd;
 	struct file *file;
@@ -133,7 +162,8 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
 		return error;
 	fd = error;
 
-	file = anon_inode_getfile(name, fops, priv, flags);
+	file = __anon_inode_getfile(name, fops, priv, flags, context_inode,
+				    secure);
 	if (IS_ERR(file)) {
 		error = PTR_ERR(file);
 		goto err_put_unused_fd;
@@ -146,8 +176,48 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
 	put_unused_fd(fd);
 	return error;
 }
+
+/**
+ * anon_inode_getfd - creates a new file instance by hooking it up to
+ *                    an anonymous inode and a dentry that describe
+ *                    the "class" of the file
+ *
+ * @name:    [in]    name of the "class" of the new file
+ * @fops:    [in]    file operations for the new file
+ * @priv:    [in]    private data for the new file (will be file's private_data)
+ * @flags:   [in]    flags
+ *
+ * Creates a new file by hooking it on a single inode. This is
+ * useful for files that do not need to have a full-fledged inode in
+ * order to operate correctly.  All the files created with
+ * anon_inode_getfd() will use the same singleton inode, reducing
+ * memory use and avoiding code duplication for the file/inode/dentry
+ * setup.  Returns a newly created file descriptor or an error code.
+ */
+int anon_inode_getfd(const char *name, const struct file_operations *fops,
+		     void *priv, int flags)
+{
+	return __anon_inode_getfd(name, fops, priv, flags, NULL, false);
+}
 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 
+/**
+ * Like anon_inode_getfd(), but creates a new !S_PRIVATE anon inode rather than
+ * reuse the singleton anon inode, and calls the inode_init_security_anon() LSM
+ * hook. This allows the inode to have its own security context and for a LSM
+ * to reject creation of the inode.  An optional @context_inode argument is
+ * also added to provide the logical relationship with the new inode.  The LSM
+ * may use @context_inode in inode_init_security_anon(), but a reference to it
+ * is not held.
+ */
+int anon_inode_getfd_secure(const char *name, const struct file_operations *fops,
+			    void *priv, int flags,
+			    const struct inode *context_inode)
+{
+	return __anon_inode_getfd(name, fops, priv, flags, context_inode, true);
+}
+EXPORT_SYMBOL_GPL(anon_inode_getfd_secure);
+
 static int __init anon_inode_init(void)
 {
 	anon_inode_mnt = kern_mount(&anon_inode_fs_type);
diff --git a/fs/libfs.c b/fs/libfs.c
index d1c3bade9f30..e52818fb276a 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1214,11 +1214,6 @@ static int anon_set_page_dirty(struct page *page)
 	return 0;
 };
 
-/*
- * A single inode exists for all anon_inode files. Contrary to pipes,
- * anon_inode inodes have no associated per-instance data, so we need
- * only allocate one of them.
- */
 struct inode *alloc_anon_inode(struct super_block *s)
 {
 	static const struct address_space_operations anon_aops = {
diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
index d0d7d96261ad..71881a2b6f78 100644
--- a/include/linux/anon_inodes.h
+++ b/include/linux/anon_inodes.h
@@ -10,12 +10,17 @@
 #define _LINUX_ANON_INODES_H
 
 struct file_operations;
+struct inode;
 
 struct file *anon_inode_getfile(const char *name,
 				const struct file_operations *fops,
 				void *priv, int flags);
 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 		     void *priv, int flags);
+int anon_inode_getfd_secure(const char *name,
+			    const struct file_operations *fops,
+			    void *priv, int flags,
+			    const struct inode *context_inode);
 
 #endif /* _LINUX_ANON_INODES_H */
 
-- 
2.30.0.284.gd98b1dd5eaa7-goog

[PATCH v14 3/4] selinux: teach SELinux about anonymous inodes

[Lokesh Gidra]

From: Daniel Colascione <dancol@google.com>

This change uses the anon_inodes and LSM infrastructure introduced in
the previous patches to give SELinux the ability to control
anonymous-inode files that are created using the new
anon_inode_getfd_secure() function.

A SELinux policy author detects and controls these anonymous inodes by
adding a name-based type_transition rule that assigns a new security
type to anonymous-inode files created in some domain. The name used
for the name-based transition is the name associated with the
anonymous inode for file listings --- e.g., "[userfaultfd]" or
"[perf_event]".

Example:

type uffd_t;
type_transition sysadm_t sysadm_t : anon_inode uffd_t "[userfaultfd]";
allow sysadm_t uffd_t:anon_inode { create };

(The next patch in this series is necessary for making userfaultfd
support this new interface.  The example above is just
for exposition.)

Signed-off-by: Daniel Colascione <dancol@google.com>
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
---
 security/selinux/hooks.c            | 59 +++++++++++++++++++++++++++++
 security/selinux/include/classmap.h |  2 +
 2 files changed, 61 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 644b17ec9e63..8b4e155b2930 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2934,6 +2933,63 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 	return 0;
 }
 
+static int selinux_inode_init_security_anon(struct inode *inode,
+					    const struct qstr *name,
+					    const struct inode *context_inode)
+{
+	const struct task_security_struct *tsec = selinux_cred(current_cred());
+	struct common_audit_data ad;
+	struct inode_security_struct *isec;
+	int rc;
+
+	if (unlikely(!selinux_initialized(&selinux_state)))
+		return 0;
+
+	isec = selinux_inode(inode);
+
+	/*
+	 * We only get here once per ephemeral inode.  The inode has
+	 * been initialized via inode_alloc_security but is otherwise
+	 * untouched.
+	 */
+	isec->initialized = LABEL_INITIALIZED;
+	isec->sclass = SECCLASS_ANON_INODE;
+
+	if (context_inode) {
+		struct inode_security_struct *context_isec =
+			selinux_inode(context_inode);
+		if (context_isec->initialized != LABEL_INITIALIZED)
+			return -EACCES;
+		if (context_isec->sclass != SECCLASS_ANON_INODE) {
+			pr_err("SELinux:  initializing anonymous inode with non-anonymous inode");
+			return -EACCES;
+		}
+
+		isec->sid = context_isec->sid;
+	} else {
+		rc = security_transition_sid(
+			&selinux_state, tsec->sid, tsec->sid,
+			isec->sclass, name, &isec->sid);
+		if (rc)
+			return rc;
+	}
+
+	/*
+	 * Now that we've initialized security, check whether we're
+	 * allowed to actually create this type of anonymous inode.
+	 */
+
+	ad.type = LSM_AUDIT_DATA_INODE;
+	ad.u.inode = inode;
+
+	return avc_has_perm(&selinux_state,
+			    tsec->sid,
+			    isec->sid,
+			    isec->sclass,
+			    ANON_INODE__CREATE,
+			    &ad);
+}
+
 static int selinux_inode_create(struct inode *dir, struct dentry *dentry, umode_t mode)
 {
 	return may_create(dir, dentry, SECCLASS_FILE);
@@ -7000,6 +7057,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 
 	LSM_HOOK_INIT(inode_free_security, selinux_inode_free_security),
 	LSM_HOOK_INIT(inode_init_security, selinux_inode_init_security),
+	LSM_HOOK_INIT(inode_init_security_anon, selinux_inode_init_security_anon),
 	LSM_HOOK_INIT(inode_create, selinux_inode_create),
 	LSM_HOOK_INIT(inode_link, selinux_inode_link),
 	LSM_HOOK_INIT(inode_unlink, selinux_inode_unlink),
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index 40cebde62856..ba2e01a6955c 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -249,6 +249,8 @@ struct security_class_mapping secclass_map[] = {
 	  {"open", "cpu", "kernel", "tracepoint", "read", "write"} },
 	{ "lockdown",
 	  { "integrity", "confidentiality", NULL } },
+	{ "anon_inode",
+	  { COMMON_FILE_PERMS, NULL } },
 	{ NULL }
   };
 
-- 
2.30.0.284.gd98b1dd5eaa7-goog

[PATCH v14 4/4] userfaultfd: use secure anon inodes for userfaultfd

[Lokesh Gidra]

From: Daniel Colascione <dancol@google.com>

This change gives userfaultfd file descriptors a real security
context, allowing policy to act on them.

Signed-off-by: Daniel Colascione <dancol@google.com>

[LG: Remove owner inode from userfaultfd_ctx]
[LG: Use anon_inode_getfd_secure() instead of anon_inode_getfile_secure()
 in userfaultfd syscall]
[LG: Use inode of file in userfaultfd_read() in resolve_userfault_fork()]

Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
---
 fs/userfaultfd.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 894cc28142e7..0be8cdd4425a 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -979,14 +979,14 @@ static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
 
 static const struct file_operations userfaultfd_fops;
 
-static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
-				  struct userfaultfd_ctx *new,
+static int resolve_userfault_fork(struct userfaultfd_ctx *new,
+				  struct inode *inode,
 				  struct uffd_msg *msg)
 {
 	int fd;
 
-	fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, new,
-			      O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS));
+	fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
+			O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
 	if (fd < 0)
 		return fd;
 
@@ -996,7 +996,7 @@ static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
 }
 
 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
-				    struct uffd_msg *msg)
+				    struct uffd_msg *msg, struct inode *inode)
 {
 	ssize_t ret;
 	DECLARE_WAITQUEUE(wait, current);
@@ -1107,7 +1107,7 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
 	spin_unlock_irq(&ctx->fd_wqh.lock);
 
 	if (!ret && msg->event == UFFD_EVENT_FORK) {
-		ret = resolve_userfault_fork(ctx, fork_nctx, msg);
+		ret = resolve_userfault_fork(fork_nctx, inode, msg);
 		spin_lock_irq(&ctx->event_wqh.lock);
 		if (!list_empty(&fork_event)) {
 			/*
@@ -1167,6 +1167,7 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf,
 	ssize_t _ret, ret = 0;
 	struct uffd_msg msg;
 	int no_wait = file->f_flags & O_NONBLOCK;
+	struct inode *inode = file_inode(file);
 
 	if (ctx->state == UFFD_STATE_WAIT_API)
 		return -EINVAL;
@@ -1174,7 +1175,7 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf,
 	for (;;) {
 		if (count < sizeof(msg))
 			return ret ? ret : -EINVAL;
-		_ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
+		_ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
 		if (_ret < 0)
 			return ret ? ret : _ret;
 		if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
@@ -1999,8 +2000,8 @@ SYSCALL_DEFINE1(userfaultfd, int, flags)
 	/* prevent the mm struct to be freed */
 	mmgrab(ctx->mm);
 
-	fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
-			      O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
+	fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
+			O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
 	if (fd < 0) {
 		mmdrop(ctx->mm);
 		kmem_cache_free(userfaultfd_ctx_cachep, ctx);
-- 
2.30.0.284.gd98b1dd5eaa7-goog

Re: [PATCH v14 3/4] selinux: teach SELinux about anonymous inodes

[Stephen Smalley]

On Fri, Jan 8, 2021 at 12:33 AM Lokesh Gidra <lokeshgidra@google.com> wrote:
>
> From: Daniel Colascione <dancol@google.com>
>
> This change uses the anon_inodes and LSM infrastructure introduced in
> the previous patches to give SELinux the ability to control
> anonymous-inode files that are created using the new
> anon_inode_getfd_secure() function.
>
> A SELinux policy author detects and controls these anonymous inodes by
> adding a name-based type_transition rule that assigns a new security
> type to anonymous-inode files created in some domain. The name used
> for the name-based transition is the name associated with the
> anonymous inode for file listings --- e.g., "[userfaultfd]" or
> "[perf_event]".
>
> Example:
>
> type uffd_t;
> type_transition sysadm_t sysadm_t : anon_inode uffd_t "[userfaultfd]";
> allow sysadm_t uffd_t:anon_inode { create };
>
> (The next patch in this series is necessary for making userfaultfd
> support this new interface.  The example above is just
> for exposition.)
>
> Signed-off-by: Daniel Colascione <dancol@google.com>
> Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
> ---
>  security/selinux/hooks.c            | 59 +++++++++++++++++++++++++++++
>  security/selinux/include/classmap.h |  2 +
>  2 files changed, 61 insertions(+)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 644b17ec9e63..8b4e155b2930 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2934,6 +2933,63 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
>         return 0;
>  }
>
> +static int selinux_inode_init_security_anon(struct inode *inode,
> +                                           const struct qstr *name,
> +                                           const struct inode *context_inode)
> +{
> +       const struct task_security_struct *tsec = selinux_cred(current_cred());
> +       struct common_audit_data ad;
> +       struct inode_security_struct *isec;
> +       int rc;
> +
> +       if (unlikely(!selinux_initialized(&selinux_state)))
> +               return 0;
> +
> +       isec = selinux_inode(inode);
> +
> +       /*
> +        * We only get here once per ephemeral inode.  The inode has
> +        * been initialized via inode_alloc_security but is otherwise
> +        * untouched.
> +        */
> +       isec->initialized = LABEL_INITIALIZED;
> +       isec->sclass = SECCLASS_ANON_INODE;
> +
> +       if (context_inode) {
> +               struct inode_security_struct *context_isec =
> +                       selinux_inode(context_inode);
> +               if (context_isec->initialized != LABEL_INITIALIZED)
> +                       return -EACCES;
> +               if (context_isec->sclass != SECCLASS_ANON_INODE) {
> +                       pr_err("SELinux:  initializing anonymous inode with non-anonymous inode");
> +                       return -EACCES;
> +               }

This would preclude using this facility for anonymous inodes created
by kvm and other use cases.
Don't do this.

> +
> +               isec->sid = context_isec->sid;
> +       } else {
> +               rc = security_transition_sid(
> +                       &selinux_state, tsec->sid, tsec->sid,
> +                       isec->sclass, name, &isec->sid);
> +               if (rc)
> +                       return rc;
> +       }
> +
> +       /*
> +        * Now that we've initialized security, check whether we're
> +        * allowed to actually create this type of anonymous inode.
> +        */
> +
> +       ad.type = LSM_AUDIT_DATA_INODE;
> +       ad.u.inode = inode;
> +
> +       return avc_has_perm(&selinux_state,
> +                           tsec->sid,
> +                           isec->sid,
> +                           isec->sclass,
> +                           ANON_INODE__CREATE,

FILE__CREATE is perfectly appropriate here, not that it makes any difference.