[PATCH 14/34] fs: Rename anon_inode_getfile_secure() and anon_inode_getfd_secure()

From: Paolo Bonzini
Date: Sun Nov 05 2023 - 11:34:07 EST

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The call to the inode_init_security_anon() LSM hook is not the sole
reason to use anon_inode_getfile_secure() or anon_inode_getfd_secure().
For example, the functions also allow one to create a file with non-zero
size, without needing a full-blown filesystem. In this case, you don't
need a "secure" version, just unique inodes; the current name of the
functions is confusing and does not explain well the difference with
the more "standard" anon_inode_getfile() and anon_inode_getfd().

Of course, there is another side of the coin; neither io_uring nor
userfaultfd strictly speaking need distinct inodes, and it is not
that clear anymore that anon_inode_create_get{file,fd}() allow the LSM
to intercept and block the inode's creation. If one was so inclined,
anon_inode_getfile_secure() and anon_inode_getfd_secure() could be kept,
using the shared inode or a new one depending on CONFIG_SECURITY.
However, this is probably overkill, and potentially a cause of bugs in
different configurations. Therefore, just add a comment to io_uring
and userfaultfd explaining the choice of the function.

While at it, remove the export for what is now anon_inode_create_getfd().
There is no in-tree module that uses it, and the old name is gone anyway.
If anybody actually needs the symbol, they can ask or they can just use
anon_inode_create_getfile(), which will be exported very soon for use
in KVM.

Suggested-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
fs/anon_inodes.c | 46 +++++++++++++++++++++++--------------
fs/userfaultfd.c | 5 ++--
include/linux/anon_inodes.h | 4 ++--
io_uring/io_uring.c | 3 ++-
4 files changed, 36 insertions(+), 22 deletions(-)

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 24192a7667ed..3d4a27f8b4fe 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -79,7 +79,7 @@ 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)
+ bool make_inode)
{
struct inode *inode;
struct file *file;
@@ -87,7 +87,7 @@ static struct file *__anon_inode_getfile(const char *name,
if (fops->owner && !try_module_get(fops->owner))
return ERR_PTR(-ENOENT);

- if (secure) {
+ if (make_inode) {
inode = anon_inode_make_secure_inode(name, context_inode);
if (IS_ERR(inode)) {
file = ERR_CAST(inode);
@@ -149,13 +149,10 @@ struct file *anon_inode_getfile(const char *name,
EXPORT_SYMBOL_GPL(anon_inode_getfile);

/**
- * anon_inode_getfile_secure - Like anon_inode_getfile(), but creates a new
+ * anon_inode_create_getfile - Like anon_inode_getfile(), 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 for both the inode to have its own
- * security context and for the LSM to enforce
- * policy on the inode's creation.
+ * inode_init_security_anon() LSM hook.
*
* @name: [in] name of the "class" of the new file
* @fops: [in] file operations for the new file
@@ -164,11 +161,19 @@ EXPORT_SYMBOL_GPL(anon_inode_getfile);
* @context_inode:
* [in] the logical relationship with the new inode (optional)
*
+ * Create a new anonymous inode and file pair. This can be done for two
+ * reasons:
+ * - for the inode to have its own security context, so that LSMs can enforce
+ * policy on the inode's creation;
+ * - if the caller needs a unique inode, for example in order to customize
+ * the size returned by fstat()
+ *
* The LSM may use @context_inode in inode_init_security_anon(), but a
- * reference to it is not held. Returns the newly created file* or an error
- * pointer. See the anon_inode_getfile() documentation for more information.
+ * reference to it is not held.
+ *
+ * Returns the newly created file* or an error pointer.
*/
-struct file *anon_inode_getfile_secure(const char *name,
+struct file *anon_inode_create_getfile(const char *name,
const struct file_operations *fops,
void *priv, int flags,
const struct inode *context_inode)
@@ -181,7 +186,7 @@ static int __anon_inode_getfd(const char *name,
const struct file_operations *fops,
void *priv, int flags,
const struct inode *context_inode,
- bool secure)
+ bool make_inode)
{
int error, fd;
struct file *file;
@@ -192,7 +197,7 @@ static int __anon_inode_getfd(const char *name,
fd = error;

file = __anon_inode_getfile(name, fops, priv, flags, context_inode,
- secure);
+ make_inode);
if (IS_ERR(file)) {
error = PTR_ERR(file);
goto err_put_unused_fd;
@@ -231,10 +236,9 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
EXPORT_SYMBOL_GPL(anon_inode_getfd);

/**
- * anon_inode_getfd_secure - Like anon_inode_getfd(), but creates a new
+ * anon_inode_create_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.
+ * the inode_init_security_anon() LSM hook.
*
* @name: [in] name of the "class" of the new file
* @fops: [in] file operations for the new file
@@ -243,16 +247,24 @@ EXPORT_SYMBOL_GPL(anon_inode_getfd);
* @context_inode:
* [in] the logical relationship with the new inode (optional)
*
+ * Create a new anonymous inode and file pair. This can be done for two
+ * reasons:
+ * - for the inode to have its own security context, so that LSMs can enforce
+ * policy on the inode's creation;
+ * - if the caller needs a unique inode, for example in order to customize
+ * the size returned by fstat()
+ *
* The LSM may use @context_inode in inode_init_security_anon(), but a
* reference to it is not held.
+ *
+ * Returns a newly created file descriptor or an error code.
*/
-int anon_inode_getfd_secure(const char *name, const struct file_operations *fops,
+int anon_inode_create_getfd(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)
{
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 56eaae9dac1a..7a1cf8bab5eb 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1033,7 +1033,7 @@ static int resolve_userfault_fork(struct userfaultfd_ctx *new,
{
int fd;

- fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
+ fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, new,
O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
if (fd < 0)
return fd;
@@ -2205,7 +2205,8 @@ static int new_userfaultfd(int flags)
/* prevent the mm struct to be freed */
mmgrab(ctx->mm);

- fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
+ /* Create a new inode so that the LSM can block the creation. */
+ fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
if (fd < 0) {
mmdrop(ctx->mm);
diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
index 5deaddbd7927..93a5f16d03f3 100644
--- a/include/linux/anon_inodes.h
+++ b/include/linux/anon_inodes.h
@@ -15,13 +15,13 @@ struct inode;
struct file *anon_inode_getfile(const char *name,
const struct file_operations *fops,
void *priv, int flags);
-struct file *anon_inode_getfile_secure(const char *name,
+struct file *anon_inode_create_getfile(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);
-int anon_inode_getfd_secure(const char *name,
+int anon_inode_create_getfd(const char *name,
const struct file_operations *fops,
void *priv, int flags,
const struct inode *context_inode);
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8d1bc6cdfe71..22b98f47bb28 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3835,7 +3835,8 @@ static struct file *io_uring_get_file(struct io_ring_ctx *ctx)
return ERR_PTR(ret);
#endif

- file = anon_inode_getfile_secure("[io_uring]", &io_uring_fops, ctx,
+ /* Create a new inode so that the LSM can block the creation. */
+ file = anon_inode_create_getfile("[io_uring]", &io_uring_fops, ctx,
O_RDWR | O_CLOEXEC, NULL);
#if defined(CONFIG_UNIX)
if (IS_ERR(file)) {
--
2.39.1

Next message: Paolo Bonzini: "[PATCH 15/34] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory"
Previous message: Paolo Bonzini: "[PATCH 13/34] mm: Add AS_UNMOVABLE to mark mapping as completely unmovable"
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Next in thread: Fuad Tabba: "Re: [PATCH 14/34] fs: Rename anon_inode_getfile_secure() and anon_inode_getfd_secure()"
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