Thread (46 messages) 46 messages, 5 authors, 2023-04-13

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

From: Paul Moore <paul@paul-moore.com>
Date: 2023-03-30 01:13:42
Also in: linux-security-module, lkml

On Wed, Mar 15, 2023 at 6:50 PM Casey Schaufler [off-list ref] wrote:
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(+)
...
quoted hunk ↗ jump to hunk
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;
I'm pretty sure this is the only place where @lsm_attr_names is used,
right?  If true, when coupled with the idea that these syscalls are
going to close the door on new LSM attributes in procfs I think we can
just put the mapping directly in this function via a series of
if-statements.
quoted hunk ↗ jump to hunk
+       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);
See my prior comments about void pointer math.
+       if (copy_to_user(ctx, &local, sizeof(local)))
+               return -EFAULT;
+       if (context_size > 0 && copy_to_user(vc, context, context_size))
+               return -EFAULT;
Should we handle the padding in this function?
+       return 0;
+}
--
paul-moore.com
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