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Subject[PATCH 2/7] Add a concept of a "secure" anonymous file
From
A secure anonymous file is one we hooked up to its own inode (as
opposed to the shared inode we use for non-secure anonymous files). A
new selinux hook gives security modules a chance to initialize, label,
and veto the creation of these secure anonymous files. Security
modules had limit ability to interact with non-secure anonymous files
due to all of these files sharing a single inode.

Signed-off-by: Daniel Colascione <dancol@google.com>
---
fs/anon_inodes.c | 45 ++++++++++++++++++++++++++++++---------
include/linux/lsm_hooks.h | 8 +++++++
include/linux/security.h | 2 ++
security/security.c | 8 +++++++
4 files changed, 53 insertions(+), 10 deletions(-)

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index caa36019afca..d68d76523ad3 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -55,6 +55,23 @@ static struct file_system_type anon_inode_fs_type = {
.kill_sb = kill_anon_super,
};

+struct inode *anon_inode_make_secure_inode(const char *name,
+ const struct file_operations *fops)
+{
+ struct inode *inode;
+ int error;
+ inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
+ if (IS_ERR(inode))
+ return ERR_PTR(PTR_ERR(inode));
+ inode->i_flags &= ~S_PRIVATE;
+ error = security_inode_init_security_anon(inode, name, fops);
+ if (error) {
+ iput(inode);
+ return ERR_PTR(error);
+ }
+ return inode;
+}
+
/**
* anon_inode_getfile2 - creates a new file instance by hooking it up to
* an anonymous inode, and a dentry that describe
@@ -72,7 +89,9 @@ static struct file_system_type anon_inode_fs_type = {
* hence saving memory and avoiding code duplication for the file/inode/dentry
* setup. Returns the newly created file* or an error pointer.
*
- * anon_inode_flags must be zero.
+ * If anon_inode_flags contains ANON_INODE_SECURE, create a new inode
+ * and enable security checks for it. Otherwise, attach a new file to
+ * a singleton placeholder inode with security checks disabled.
*/
struct file *anon_inode_getfile2(const char *name,
const struct file_operations *fops,
@@ -81,17 +100,23 @@ struct file *anon_inode_getfile2(const char *name,
struct inode *inode;
struct file *file;

- if (anon_inode_flags)
+ if (anon_inode_flags & ~ANON_INODE_SECURE)
return ERR_PTR(-EINVAL);

- inode = anon_inode_inode;
- if (IS_ERR(inode))
- return ERR_PTR(-ENODEV);
- /*
- * We know the anon_inode inode count is always
- * greater than zero, so ihold() is safe.
- */
- ihold(inode);
+ if (anon_inode_flags & ANON_INODE_SECURE) {
+ inode = anon_inode_make_secure_inode(name, fops);
+ if (IS_ERR(inode))
+ return ERR_PTR(PTR_ERR(inode));
+ } else {
+ inode = anon_inode_inode;
+ if (IS_ERR(inode))
+ return ERR_PTR(-ENODEV);
+ /*
+ * We know the anon_inode inode count is always
+ * greater than zero, so ihold() is safe.
+ */
+ ihold(inode);
+ }

if (fops->owner && !try_module_get(fops->owner)) {
file = ERR_PTR(-ENOENT);
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index a3763247547c..3744ce9e9172 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -215,6 +215,10 @@
* 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 a secure anonymous inode.
+ * Returns 0 on success. Returns -EPERM if the security module denies
+ * the creation of this inode.
* @inode_create:
* Check permission to create a regular file.
* @dir contains inode structure of the parent of the new file.
@@ -1552,6 +1556,9 @@ union security_list_options {
const struct qstr *qstr,
const char **name, void **value,
size_t *len);
+ int (*inode_init_security_anon)(struct inode *inode,
+ const char *name,
+ const struct file_operations *fops);
int (*inode_create)(struct inode *dir, struct dentry *dentry,
umode_t mode);
int (*inode_link)(struct dentry *old_dentry, struct inode *dir,
@@ -1876,6 +1883,7 @@ struct security_hook_heads {
struct hlist_head inode_alloc_security;
struct hlist_head inode_free_security;
struct hlist_head inode_init_security;
+ struct hlist_head inode_init_security_anon;
struct hlist_head inode_create;
struct hlist_head inode_link;
struct hlist_head inode_unlink;
diff --git a/include/linux/security.h b/include/linux/security.h
index a8d59d612d27..5b6f7e0de577 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -315,6 +315,8 @@ 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 char *name,
+ const struct file_operations *fops);
int security_old_inode_init_security(struct inode *inode, struct inode *dir,
const struct qstr *qstr, const char **name,
void **value, size_t *len);
diff --git a/security/security.c b/security/security.c
index 1bc000f834e2..c87695f66413 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1001,6 +1001,14 @@ 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 char *name,
+ const struct file_operations *fops)
+{
+ return call_int_hook(inode_init_security_anon, 0, inode, name, fops);
+}
+
int security_old_inode_init_security(struct inode *inode, struct inode *dir,
const struct qstr *qstr, const char **name,
void **value, size_t *len)
--
2.23.0.700.g56cf767bdb-goog
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