cred: Add a light version of override/revert_creds()

Add a light version of override/revert_creds(), this should only be
used when the credentials in question will outlive the critical
section and the critical section doesn't change the ->usage of the
credentials.

Suggested-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/cred.h b/include/linux/cred.h
index 2976f534a7a3..e4a3155fe409 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -172,6 +172,24 @@ static inline bool cap_ambient_invariant_ok(const struct cred *cred)
 					  cred->cap_inheritable));
 }
 
+/*
+ * Override creds without bumping reference count. Caller must ensure
+ * reference remains valid or has taken reference. Almost always not the
+ * interface you want. Use override_creds()/revert_creds() instead.
+ */
+static inline const struct cred *override_creds_light(const struct cred *override_cred)
+{
+	const struct cred *old = current->cred;
+
+	rcu_assign_pointer(current->cred, override_cred);
+	return old;
+}
+
+static inline void revert_creds_light(const struct cred *revert_cred)
+{
+	rcu_assign_pointer(current->cred, revert_cred);
+}
+
 /**
  * get_new_cred_many - Get references on a new set of credentials
  * @cred: The new credentials to reference