[PATCH v8 07/11] LSM: Helpers for attribute names and filling an lsm_ctx

[Casey Schaufler]

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. The .len value is padded to a multiple
of the size of the structure for alignment.

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

Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
---
 include/linux/security.h | 13 +++++++++++
 security/lsm_syscalls.c  | 24 ++++++++++++++++++++
 security/security.c      | 48 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 85 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index f7292890b6a2..c96fb56159e3 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..67106f642422 100644
--- a/security/lsm_syscalls.c
+++ b/security/lsm_syscalls.c
@@ -17,6 +17,30 @@
 #include <linux/lsm_hooks.h>
 #include <uapi/linux/lsm.h>
 
+/**
+ * lsm_name_to_attr - map an LSM attribute name to its ID
+ * @name: name of the attribute
+ *
+ * Returns the LSM attribute value associated with @name, or 0 if
+ * there is no mapping.
+ */
+u64 lsm_name_to_attr(const char *name)
+{
+	if (!strcmp(name, "current"))
+		return LSM_ATTR_CURRENT;
+	if (!strcmp(name, "exec"))
+		return LSM_ATTR_EXEC;
+	if (!strcmp(name, "fscreate"))
+		return LSM_ATTR_FSCREATE;
+	if (!strcmp(name, "keycreate"))
+		return LSM_ATTR_KEYCREATE;
+	if (!strcmp(name, "prev"))
+		return LSM_ATTR_PREV;
+	if (!strcmp(name, "sockcreate"))
+		return LSM_ATTR_SOCKCREATE;
+	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 bfe9a1a426b2..453f3ff591ec 100644
--- a/security/security.c
+++ b/security/security.c
@@ -752,6 +752,54 @@ 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.
+ *
+ * The total length is padded to an integral number of lsm_ctx.
+ *
+ * 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 *lctx;
+	size_t locallen;
+	u8 *composite;
+	int rc = 0;
+
+	locallen = sizeof(*ctx);
+	if (context_size)
+		locallen += sizeof(*ctx) * ((context_size / sizeof(*ctx)) + 1);
+
+	composite = kzalloc(locallen, GFP_KERNEL);
+	if (composite == NULL)
+		return -ENOMEM;
+
+	lctx = (struct lsm_ctx *)composite;
+	lctx->id = id;
+	lctx->flags = flags;
+	lctx->ctx_len = context_size;
+	lctx->len = locallen;
+
+	memcpy(composite + sizeof(*lctx), context, context_size);
+
+	if (copy_to_user(ctx, composite, locallen))
+		rc = -EFAULT;
+
+	kfree(composite);
+
+	return rc;
+}
+
 /*
  * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
  * can be accessed with:
-- 
2.39.2