[RFC PATCH 9/9] Smack: Brutalist io_uring support with debug

Paul Moore
2021-05-21T21:50:40Z

From: Casey Schaufler <casey@schaufler-ca.com>

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>
Signed-off-by: Paul Moore <paul@paul-moore.com>
---
security/smack/smack_lsm.c | 64 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 64 insertions(+)

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 223a6da0e6dc..f6423c0096e9 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4691,6 +4691,66 @@ 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.
+ */
+int smack_uring_override_creds(const struct cred *new)
+{
+ struct task_smack *tsp = smack_cred(current_cred());
+ struct task_smack *nsp = smack_cred(new);
+
+#if 1
+ if (tsp->smk_task == nsp->smk_task)
+ pr_info("%s: Smack matches %s\n", __func__,
+ tsp->smk_task->smk_known);
+ else
+ pr_info("%s: Smack override check %s to %s\n", __func__,
+ tsp->smk_task->smk_known, nsp->smk_task->smk_known);
+#endif
+ /*
+ * 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 1
+ pr_info("%s: Smack sqpoll %s\n", __func__,
+ smack_privileged_cred(CAP_MAC_OVERRIDE, current_cred()) ?
+ "ok by Smack" : "disallowed (No CAP_MAC_OVERRIDE)");
+#endif
+ 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.
+ */
+int smack_uring_sqpoll(void)
+{
+#if 1
+ pr_info("%s: Smack new ring %s\n", __func__,
+ smack_privileged_cred(CAP_MAC_ADMIN, current_cred()) ?
+ "ok by Smack" : "disallowed (No CAP_MAC_ADMIN)");
+#endif
+ 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 +4903,10 @@ 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
};