[PATCH v7 07/11] LSM: Helpers for attribute names and filling an lsm_ctx

[Casey Schaufler <casey@schaufler-ca.com>]

Add lsm_name_to_attr(), which translates a text string to a
LSM_ATTR value if one is available.

Add lsm_fill_user_ctx(), which fills a struct lsm_ctx, including
the trailing attribute value.

All are used in module specific components of LSM system calls.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 include/linux/security.h | 13 ++++++++++
 security/lsm_syscalls.c  | 51 ++++++++++++++++++++++++++++++++++++++++
 security/security.c      | 31 ++++++++++++++++++++++++
 3 files changed, 95 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 329cd9d2be50..a5e860d332b5 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -263,6 +263,7 @@ int unregister_blocking_lsm_notifier(struct notifier_block *nb);
 /* prototypes */
 extern int security_init(void);
 extern int early_security_init(void);
+extern u64 lsm_name_to_attr(const char *name);
 
 /* Security operations */
 int security_binder_set_context_mgr(const struct cred *mgr);
@@ -491,6 +492,8 @@ int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
 int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
 int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
 int security_locked_down(enum lockdown_reason what);
+int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
+		      size_t context_size, u64 id, u64 flags);
 #else /* CONFIG_SECURITY */
 
 static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
@@ -508,6 +511,11 @@ static inline  int unregister_blocking_lsm_notifier(struct notifier_block *nb)
 	return 0;
 }
 
+static inline u64 lsm_name_to_attr(const char *name)
+{
+	return 0;
+}
+
 static inline void security_free_mnt_opts(void **mnt_opts)
 {
 }
@@ -1420,6 +1428,11 @@ static inline int security_locked_down(enum lockdown_reason what)
 {
 	return 0;
 }
+static inline int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
+				    size_t context_size, u64 id, u64 flags)
+{
+	return 0;
+}
 #endif	/* CONFIG_SECURITY */
 
 #if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
index 6efbe244d304..55d849ad5d6e 100644
--- a/security/lsm_syscalls.c
+++ b/security/lsm_syscalls.c
@@ -17,6 +17,57 @@
 #include <linux/lsm_hooks.h>
 #include <uapi/linux/lsm.h>
 
+struct attr_map {
+	char *name;
+	u64 attr;
+};
+
+static const struct attr_map lsm_attr_names[] = {
+	{
+		.name = "current",
+		.attr = LSM_ATTR_CURRENT,
+	},
+	{
+		.name = "exec",
+		.attr = LSM_ATTR_EXEC,
+	},
+	{
+		.name = "fscreate",
+		.attr = LSM_ATTR_FSCREATE,
+	},
+	{
+		.name = "keycreate",
+		.attr = LSM_ATTR_KEYCREATE,
+	},
+	{
+		.name = "prev",
+		.attr = LSM_ATTR_PREV,
+	},
+	{
+		.name = "sockcreate",
+		.attr = LSM_ATTR_SOCKCREATE,
+	},
+};
+
+/**
+ * lsm_name_to_attr - map an LSM attribute name to its ID
+ * @name: name of the attribute
+ *
+ * Look the given @name up in the table of know attribute names.
+ *
+ * Returns the LSM attribute value associated with @name, or 0 if
+ * there is no mapping.
+ */
+u64 lsm_name_to_attr(const char *name)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(lsm_attr_names); i++)
+		if (!strcmp(name, lsm_attr_names[i].name))
+			return lsm_attr_names[i].attr;
+	return 0;
+}
+
 /**
  * sys_lsm_set_self_attr - Set current task's security module attribute
  * @attr: which attribute to set
diff --git a/security/security.c b/security/security.c
index 2c57fe28c4f7..f7b814a3940c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -753,6 +753,37 @@ static int lsm_superblock_alloc(struct super_block *sb)
 	return 0;
 }
 
+/**
+ * lsm_fill_user_ctx - Fill a user space lsm_ctx structure
+ * @ctx: an LSM context to be filled
+ * @context: the new context value
+ * @context_size: the size of the new context value
+ * @id: LSM id
+ * @flags: LSM defined flags
+ *
+ * Fill all of the fields in a user space lsm_ctx structure.
+ * Caller is assumed to have verified that @ctx has enough space
+ * for @context.
+ * Returns 0 on success, -EFAULT on a copyout error.
+ */
+int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
+		      size_t context_size, u64 id, u64 flags)
+{
+	struct lsm_ctx local;
+	void __user *vc = ctx;
+
+	local.id = id;
+	local.flags = flags;
+	local.ctx_len = context_size;
+	local.len = context_size + sizeof(local);
+	vc += sizeof(local);
+	if (copy_to_user(ctx, &local, sizeof(local)))
+		return -EFAULT;
+	if (context_size > 0 && copy_to_user(vc, context, context_size))
+		return -EFAULT;
+	return 0;
+}
+
 /*
  * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
  * can be accessed with:
-- 
2.39.2