[PATCH 1/5] Security: Provide copy-up security hooks for unioned files

David Howells
2015-09-28T20:00:39Z

Provide two new security hooks for use with security files that are used when
a file is copied up between layers:

(1) security_inode_copy_up(). This is called so that the security label on
the destination file can be set appropriately.

(2) security_inode_copy_up_xattr(). This is called so that each xattr being
copied up can be vetted - including modification and discard.

Signed-off-by: David Howells <dhowells@redhat.com>
---

include/linux/lsm_hooks.h | 23 +++++++++++++++++++++++
include/linux/security.h | 14 ++++++++++++++
security/security.c | 17 +++++++++++++++++
3 files changed, 54 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index ec3a6bab29de..8c0c524dd232 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -401,6 +401,24 @@
* @inode contains a pointer to the inode.
* @secid contains a pointer to the location where result will be saved.
* In case of failure, @secid will be set to zero.
+ * @inode_copy_up:
+ * Appropriately label the destination inode when a unioned file is copied
+ * up from a lower layer to the union/overlay layer.
+ * @src indicates the file that is being copied up.
+ * @dst indicates the file that has being created by the copy up.
+ * Returns 0 on success or a negative error code on error.
+ * @inode_copy_up_xattr:
+ * Filter/modify the xattrs being copied up when a unioned file is copied
+ * up from a lower layer to the union/overlay layer.
+ * @src indicates the file that is being copied up.
+ * @dst indicates the file that has being created by the copy up.
+ * @name indicates the name of the xattr.
+ * @value, *@size indicate the payload of the xattr.
+ * Returns 0 to accept the xattr, 1 to discard the xattr or a negative
+ * error code to abort the copy up. The xattr buffer must be at least
+ * XATTR_SIZE_MAX in capacity and the contents may be modified and *@size
+ * changed appropriately. Note that the caller is responsible for reading
+ * and writing the xattrs as this hook is merely a filter.
*
* Security hooks for file operations
*
@@ -1421,6 +1439,9 @@ union security_list_options {
int (*inode_listsecurity)(struct inode *inode, char *buffer,
size_t buffer_size);
void (*inode_getsecid)(const struct inode *inode, u32 *secid);
+ int (*inode_copy_up) (struct dentry *src, struct dentry *dst);
+ int (*inode_copy_up_xattr) (struct dentry *src, struct dentry *dst,
+ const char *name, void *value, size_t *size);

int (*file_permission)(struct file *file, int mask);
int (*file_alloc_security)(struct file *file);
@@ -1689,6 +1710,8 @@ struct security_hook_heads {
struct list_head inode_setsecurity;
struct list_head inode_listsecurity;
struct list_head inode_getsecid;
+ struct list_head inode_copy_up;
+ struct list_head inode_copy_up_xattr;
struct list_head file_permission;
struct list_head file_alloc_security;
struct list_head file_free_security;
diff --git a/include/linux/security.h b/include/linux/security.h
index 2f4c1f7aa7db..ec21144d8807 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -274,6 +274,10 @@ int security_inode_getsecurity(const struct inode *inode, const char *name, void
int security_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags);
int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size);
void security_inode_getsecid(const struct inode *inode, u32 *secid);
+int security_inode_copy_up(struct dentry *src, struct dentry *dst);
+int security_inode_copy_up_xattr(struct dentry *src, struct dentry *dst,
+ const char *name, void *value, size_t *size);
+
int security_file_permission(struct file *file, int mask);
int security_file_alloc(struct file *file);
void security_file_free(struct file *file);
@@ -739,6 +743,16 @@ static inline void security_inode_getsecid(const struct inode *inode, u32 *secid
*secid = 0;
}

+static inline int security_inode_copy_up(struct dentry *src, struct dentry *dst)
+{
+ return 0;
+}
+static inline int security_inode_copy_up_xattr(struct dentry *src, struct dentry *dst,
+ const char *name, const void *value, size_t *size)
+{
+ return 0;
+}
+
static inline int security_file_permission(struct file *file, int mask)
{
return 0;
diff --git a/security/security.c b/security/security.c
index 46f405ce6b0f..e33c5d5bdc6b 100644
--- a/security/security.c
+++ b/security/security.c
@@ -726,6 +726,19 @@ void security_inode_getsecid(const struct inode *inode, u32 *secid)
call_void_hook(inode_getsecid, inode, secid);
}

+int security_inode_copy_up(struct dentry *src, struct dentry *dst)
+{
+ return call_int_hook(inode_copy_up, 0, src, dst);
+}
+EXPORT_SYMBOL(security_inode_copy_up);
+
+int security_inode_copy_up_xattr(struct dentry *src, struct dentry *dst,
+ const char *name, void *value, size_t *size)
+{
+ return call_int_hook(inode_copy_up_xattr, 0, src, dst, name, value, size);
+}
+EXPORT_SYMBOL(security_inode_copy_up_xattr);
+
int security_file_permission(struct file *file, int mask)
{
int ret;
@@ -1654,6 +1667,10 @@ struct security_hook_heads security_hook_heads = {
LIST_HEAD_INIT(security_hook_heads.inode_listsecurity),
.inode_getsecid =
LIST_HEAD_INIT(security_hook_heads.inode_getsecid),
+ .inode_copy_up =
+ LIST_HEAD_INIT(security_hook_heads.inode_copy_up),
+ .inode_copy_up_xattr =
+ LIST_HEAD_INIT(security_hook_heads.inode_copy_up_xattr),
.file_permission =
LIST_HEAD_INIT(security_hook_heads.file_permission),
.file_alloc_security =