Smack: Brutalist io_uring support

Add Smack privilege checks for io_uring. Use CAP_MAC_OVERRIDE
for the override_creds case and CAP_MAC_ADMIN for creating a
polling thread. These choices are based on conjecture regarding
the intent of the surrounding code.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
[PM: make the smack_uring_* funcs static, remove debug code]
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index cacbe751851943ea022ffa9054befe9102b77fb5..f90ab1efeb6d8284aaeb7565dab1834a2096779d 100644 (file)
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4691,6 +4691,48 @@ static int smack_dentry_create_files_as(struct dentry *dentry, int mode,
        return 0;
 }
 
+#ifdef CONFIG_IO_URING
+/**
+ * smack_uring_override_creds - Is io_uring cred override allowed?
+ * @new: the target creds
+ *
+ * Check to see if the current task is allowed to override it's credentials
+ * to service an io_uring operation.
+ */
+static int smack_uring_override_creds(const struct cred *new)
+{
+       struct task_smack *tsp = smack_cred(current_cred());
+       struct task_smack *nsp = smack_cred(new);
+
+       /*
+        * Allow the degenerate case where the new Smack value is
+        * the same as the current Smack value.
+        */
+       if (tsp->smk_task == nsp->smk_task)
+               return 0;
+
+       if (smack_privileged_cred(CAP_MAC_OVERRIDE, current_cred()))
+               return 0;
+
+       return -EPERM;
+}
+
+/**
+ * smack_uring_sqpoll - check if a io_uring polling thread can be created
+ *
+ * Check to see if the current task is allowed to create a new io_uring
+ * kernel polling thread.
+ */
+static int smack_uring_sqpoll(void)
+{
+       if (smack_privileged_cred(CAP_MAC_ADMIN, current_cred()))
+               return 0;
+
+       return -EPERM;
+}
+
+#endif /* CONFIG_IO_URING */
+
 struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init = {
        .lbs_cred = sizeof(struct task_smack),
        .lbs_file = sizeof(struct smack_known *),
@@ -4843,6 +4885,10 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
        LSM_HOOK_INIT(inode_copy_up, smack_inode_copy_up),
        LSM_HOOK_INIT(inode_copy_up_xattr, smack_inode_copy_up_xattr),
        LSM_HOOK_INIT(dentry_create_files_as, smack_dentry_create_files_as),
+#ifdef CONFIG_IO_URING
+       LSM_HOOK_INIT(uring_override_creds, smack_uring_override_creds),
+       LSM_HOOK_INIT(uring_sqpoll, smack_uring_sqpoll),
+#endif
 };