[PATCH v13 07/11] LSM: Helpers for attribute names and filling lsm_ctx

Casey Schaufler
2023-08-02T17:48:41Z

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.

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

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
---
include/linux/security.h | 14 ++++++++++++++
security/lsm_syscalls.c | 24 +++++++++++++++++++++++
security/security.c | 41 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 79 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 0d882cb221f4..817cf28dbf8a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -32,6 +32,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/sockptr.h>
+#include <uapi/linux/lsm.h>

struct linux_binprm;
struct cred;
@@ -263,6 +264,7 @@ 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);
@@ -488,6 +490,8 @@ 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)
@@ -505,6 +509,11 @@ static inline int unregister_blocking_lsm_notifier(struct notifier_block *nb)
return 0;
}

+static inline u64 lsm_name_to_attr(const char *name)
+{
+ return LSM_ATTR_UNDEF;
+}
+
static inline void security_free_mnt_opts(void **mnt_opts)
{
}
@@ -1408,6 +1417,11 @@ 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 -EOPNOTSUPP;
+}
#endif /* CONFIG_SECURITY */

#if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
index f03f2d17ab49..bc22f05e2d8c 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 LSM_ATTR_UNDEF;
+}
+
/**
* 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 cde7f3a13e7c..f1038686ebd0 100644
--- a/security/security.c
+++ b/security/security.c
@@ -770,6 +770,47 @@ 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, -ENOMEM
+ * if memory can't be allocated.
+ */
+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 = struct_size(lctx, ctx, context_size);
+ int rc = 0;
+
+ lctx = kzalloc(locallen, GFP_KERNEL);
+ if (lctx == NULL)
+ return -ENOMEM;
+
+ lctx->id = id;
+ lctx->flags = flags;
+ lctx->ctx_len = context_size;
+ lctx->len = locallen;
+
+ memcpy(lctx->ctx, context, context_size);
+
+ if (copy_to_user(ctx, lctx, locallen))
+ rc = -EFAULT;
+
+ kfree(lctx);
+
+ return rc;
+}
+
/*
* The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
* can be accessed with:
--
2.41.0