linux-kernel - [PATCH v2 06/16] cred: Introduce cred_guard() and cred_scoped

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Message-ID: <20240822012523.141846-7-vinicius.gomes@intel.com>
Date: Wed, 21 Aug 2024 18:25:13 -0700
From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
To: brauner@...nel.org,
	amir73il@...il.com,
	hu1.chen@...el.com
Cc: miklos@...redi.hu,
	malini.bhandaru@...el.com,
	tim.c.chen@...el.com,
	mikko.ylinen@...el.com,
	lizhen.you@...el.com,
	linux-unionfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Vinicius Costa Gomes <vinicius.gomes@...el.com>
Subject: [PATCH v2 06/16] cred: Introduce cred_guard() and cred_scoped_guard() helpers

These helpers will make it less error prone to use
override_creds_light()/revert_creds_light(). They make sure that they
are paired.

As they use the _light() version of the credentials override/revert
operations, they should only be used when there are guarantees that
the lifetime of the credentials in question is not modified during the
critical section.

Suggested-by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
---
 include/linux/cred.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/cred.h b/include/linux/cred.h
index e4a3155fe409..f4f3d55cd6a2 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -190,6 +190,13 @@ static inline void revert_creds_light(const struct cred *revert_cred)
 	rcu_assign_pointer(current->cred, revert_cred);
 }
 
+DEFINE_LOCK_GUARD_1(__cred, struct cred,
+		    _T->lock = (struct cred *)override_creds_light(_T->lock),
+		    revert_creds_light(_T->lock));
+
+#define cred_guard(_cred) guard(__cred)(((struct cred *)_cred))
+#define cred_scoped_guard(_cred) scoped_guard(__cred, ((struct cred *)_cred))
+
 /**
  * get_new_cred_many - Get references on a new set of credentials
  * @cred: The new credentials to reference
-- 
2.46.0