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()
[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/linux-fsdevel/[email protected]/
[3] https://lore.kernel.org/lkml/[email protected]/
Daniel Colascione (3):
Add a new LSM-supporting anonymous inode interface
Teach SELinux about anonymous inodes
Use secure anon inodes for userfaultfd
fs/anon_inodes.c | 148 ++++++++++++++++++++--------
fs/userfaultfd.c | 19 ++--
include/linux/anon_inodes.h | 8 ++
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 | 53 ++++++++++
security/selinux/include/classmap.h | 2 +
9 files changed, 210 insertions(+), 49 deletions(-)
--
2.28.0.1011.ga647a8990f-goog
From: Daniel Colascione <[email protected]>
This change uses the anon_inodes and LSM infrastructure introduced in
the previous patch 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 <[email protected]>
Signed-off-by: Lokesh Gidra <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andrew Morton <[email protected]>
---
security/selinux/hooks.c | 53 +++++++++++++++++++++++++++++
security/selinux/include/classmap.h | 2 ++
2 files changed, 55 insertions(+)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index a340986aa92e..7b22c3112583 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2926,6 +2926,58 @@ 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.
+ */
+
+ if (context_inode) {
+ struct inode_security_struct *context_isec =
+ selinux_inode(context_inode);
+ isec->sclass = context_isec->sclass;
+ isec->sid = context_isec->sid;
+ } else {
+ isec->sclass = SECCLASS_ANON_INODE;
+ rc = security_transition_sid(
+ &selinux_state, tsec->sid, tsec->sid,
+ isec->sclass, name, &isec->sid);
+ if (rc)
+ return rc;
+ }
+
+ isec->initialized = LABEL_INITIALIZED;
+
+ /*
+ * 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,
+ FILE__CREATE,
+ &ad);
+}
+
static int selinux_inode_create(struct inode *dir, struct dentry *dentry, umode_t mode)
{
return may_create(dir, dentry, SECCLASS_FILE);
@@ -6987,6 +7039,7 @@ 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 }
};
--
2.28.0.1011.ga647a8990f-goog
From: Daniel Colascione <[email protected]>
This change gives userfaultfd file descriptors a real security
context, allowing policy to act on them.
Signed-off-by: Daniel Colascione <[email protected]>
[Remove owner inode from userfaultfd_ctx]
[Use anon_inode_getfd_secure() instead of anon_inode_getfile_secure()
in userfaultfd syscall]
[Use inode of file in userfaultfd_read() in resolve_userfault_fork()]
Signed-off-by: Lokesh Gidra <[email protected]>
---
fs/userfaultfd.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 0e4a3837da52..918535b49475 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -978,14 +978,14 @@ 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;
@@ -995,7 +995,7 @@ 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);
@@ -1106,7 +1106,7 @@ 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)) {
/*
@@ -1166,6 +1166,7 @@ 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;
@@ -1173,7 +1174,7 @@ 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)))
@@ -1995,8 +1996,8 @@ 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);
--
2.28.0.1011.ga647a8990f-goog
From: Daniel Colascione <[email protected]>
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 granting/denying permission to create an anon inode
of the same type.
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 <[email protected]>
[Fix comment documenting return values of inode_init_security_anon()]
[Add context_inode description in comments to anon_inode_getfd_secure()]
[Remove definition of anon_inode_getfile_secure() as there are no callers]
[Make __anon_inode_getfile() static]
[Use correct error cast in __anon_inode_getfile()]
[Fix error handling in __anon_inode_getfile()]
Signed-off-by: Lokesh Gidra <[email protected]>
---
fs/anon_inodes.c | 148 +++++++++++++++++++++++++---------
include/linux/anon_inodes.h | 8 ++
include/linux/lsm_hook_defs.h | 2 +
include/linux/lsm_hooks.h | 9 +++
include/linux/security.h | 10 +++
security/security.c | 8 ++
6 files changed, 145 insertions(+), 40 deletions(-)
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 89714308c25b..a3fe08fcaa52 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 +176,46 @@ 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() creates a new file, but by hooking it to a new anon
+ * inode, rather than to the same singleton inode. Also adds the @context_inode
+ * argument to allow security modules to control creation of the new file. Once
+ * the security module makes the decision, the context_inode is no longer needed
+ * and hence 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/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
index d0d7d96261ad..6ab840ee93bc 100644
--- a/include/linux/anon_inodes.h
+++ b/include/linux/anon_inodes.h
@@ -10,12 +10,20 @@
#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_secure(const char *name,
+ const struct file_operations *fops,
+ void *priv, int flags,
+ const struct inode *context_inode);
+
int anon_inode_getfd(const char *name, const struct file_operations *fops,
void *priv, int flags);
+
#endif /* _LINUX_ANON_INODES_H */
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 2a8c74d99015..35ff75c43de4 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 9e2e3e63719d..586186f1184b 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, -EACCESS 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 0a0a03b36a3b..7c6b3dcf4721 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -322,6 +322,9 @@ 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);
@@ -732,6 +735,13 @@ 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 70a7ad357bc6..2c4b121a01b9 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1057,6 +1057,14 @@ 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)
--
2.28.0.1011.ga647a8990f-goog
On Sun, Oct 11, 2020 at 1:29 AM Lokesh Gidra <[email protected]> wrote:
>
> 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()
>
> [1] https://lore.kernel.org/lkml/[email protected]/
> [2] https://lore.kernel.org/linux-fsdevel/[email protected]/
> [3] https://lore.kernel.org/lkml/[email protected]/
>
> Daniel Colascione (3):
> Add a new LSM-supporting anonymous inode interface
> Teach SELinux about anonymous inodes
> Use secure anon inodes for userfaultfd
>
> fs/anon_inodes.c | 148 ++++++++++++++++++++--------
> fs/userfaultfd.c | 19 ++--
> include/linux/anon_inodes.h | 8 ++
> 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 | 53 ++++++++++
> security/selinux/include/classmap.h | 2 +
> 9 files changed, 210 insertions(+), 49 deletions(-)
>
> --
> 2.28.0.1011.ga647a8990f-goog
>
Any suggestions on how to get VFS folks' (already CC'ed) attention on
this patch series?
In the meantime, I humbly request the SELinux/LSM/UFFD
reviewers/maintainers to provide their reviews.
On Sun, Oct 11, 2020 at 01:29:33AM -0700, Lokesh Gidra wrote:
> Daniel Colascione (3):
> Add a new LSM-supporting anonymous inode interface
> Teach SELinux about anonymous inodes
> Use secure anon inodes for userfaultfd
Patches are supposed to have subsystem prefixes, e.g.
fs, security: add a new LSM-supporting anonymous inode interface
selinux: implement init_security_anon()
userfaultfd: use secure anon inodes
... but that points to the fact that the first one is really both fs and
security subsystem changes. Patches should be one logical change only. I
suggest splitting it up into:
security: add init_security_anon() LSM hook
fs: add anon_inode_getfd_secure()
- Eric
On Wed, Nov 04, 2020 at 12:07:16PM -0800, Eric Biggers wrote:
> On Sun, Oct 11, 2020 at 01:29:33AM -0700, Lokesh Gidra wrote:
> > Daniel Colascione (3):
> > Add a new LSM-supporting anonymous inode interface
> > Teach SELinux about anonymous inodes
> > Use secure anon inodes for userfaultfd
>
> Patches are supposed to have subsystem prefixes, e.g.
>
> fs, security: add a new LSM-supporting anonymous inode interface
> selinux: implement init_security_anon()
> userfaultfd: use secure anon inodes
>
> ... but that points to the fact that the first one is really both fs and
> security subsystem changes. Patches should be one logical change only. I
> suggest splitting it up into:
>
> security: add init_security_anon() LSM hook
> fs: add anon_inode_getfd_secure()
Correction: it's "inode_init_security_anon()", not "init_security_anon()".
- Eric
On Sun, Oct 11, 2020 at 01:29:36AM -0700, Lokesh Gidra wrote:
> From: Daniel Colascione <[email protected]>
>
> This change gives userfaultfd file descriptors a real security
> context, allowing policy to act on them.
>
> Signed-off-by: Daniel Colascione <[email protected]>
>
> [Remove owner inode from userfaultfd_ctx]
> [Use anon_inode_getfd_secure() instead of anon_inode_getfile_secure()
> in userfaultfd syscall]
> [Use inode of file in userfaultfd_read() in resolve_userfault_fork()]
>
> Signed-off-by: Lokesh Gidra <[email protected]>
> ---
I'm not an expert in userfaultfd or SELinux, but I don't see any issues with
this patch, and the comments I made earlier were resolved (except for the patch
title which I just pointed out -- it should have "userfaultfd:" prefix).
So feel free to add:
Reviewed-by: Eric Biggers <[email protected]>
At a high level this patch looks fine to me, but a few nits below. Also as I
mentioned on the cover letter, it seems this should be split into two patches --
one for the fs changes and one for the security changes.
On Sun, Oct 11, 2020 at 01:29:34AM -0700, Lokesh Gidra wrote:
> +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;
The comment for alloc_anon_inode() still claims that it uses a single inode.
It would be helpful to fix that comment.
> +/**
> + * Like anon_inode_getfd() creates a new file, but by hooking it to a new anon
> + * inode, rather than to the same singleton inode. Also adds the @context_inode
> + * argument to allow security modules to control creation of the new file. Once
> + * the security module makes the decision, the context_inode is no longer needed
> + * and hence reference to it is not held.
> + */
The first sentence seems a bit off, gramatically. Also, it seems there should
be a hint here as to why anyone would care whether the inode is singleton or
not. Remember, people will be reading this code years down the line, and people
may not understand the exact problem you are trying to solve.
Would the following be accurate, or am I misunderstanding something?
/**
* Like anon_inode_getfd(), but create a new !S_PRIVATE anon inode rather than
* reuse the singleton anon inode, and call the 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 "parent" of the new inode. The LSM may use
* @context_inode in init_security_anon(), but a reference to it is not held.
*/
> diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
> index d0d7d96261ad..6ab840ee93bc 100644
> --- a/include/linux/anon_inodes.h
> +++ b/include/linux/anon_inodes.h
> @@ -10,12 +10,20 @@
> #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_secure(const char *name,
> + const struct file_operations *fops,
> + void *priv, int flags,
> + const struct inode *context_inode);
> +
> int anon_inode_getfd(const char *name, const struct file_operations *fops,
> void *priv, int flags);
>
> +
Unwanted whitespace change here.
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 9e2e3e63719d..586186f1184b 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, -EACCESS if the security module denies the
> + * creation of this inode, or another -errno upon other errors.
EACCES, not EACCESS. The spelling mistakes of decades past are still with us...
- Eric