[PATCH 6.18.y 2/3] cred: add scoped_with_kernel_creds()

[Sasha Levin <sashal@kernel.org>]

From: Christian Brauner <brauner@kernel.org>

[ Upstream commit ae40e6c65791f47c76cc14d0cce2707fe6053f72 ]

Add a new cleanup class for override creds. We can make use of this in a
bunch of places going forward.

Based on this scoped_with_kernel_creds() that can be used to temporarily
assume kernel credentials for specific tasks such as firmware loading,
or coredump socket connections. At no point will the caller interact
with the kernel credentials directly.

Link: https://patch.msgid.link/20251103-work-creds-init_cred-v1-4-cb3ec8711a6a@kernel.org
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Stable-dep-of: 981ccd97f715 ("dm: avoid leaking the caller's thread keyring via the table device file")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/cred.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/cred.h b/include/linux/cred.h
index 8ab3718184adf8..be2cd07b174c5e 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -187,6 +187,14 @@ static inline const struct cred *revert_creds(const struct cred *revert_cred)
 	return rcu_replace_pointer(current->cred, revert_cred, 1);
 }
 
+DEFINE_CLASS(override_creds,
+	     const struct cred *,
+	     revert_creds(_T),
+	     override_creds(override_cred), const struct cred *override_cred)
+
+#define scoped_with_kernel_creds() \
+	scoped_class(override_creds, __UNIQUE_ID(cred), kernel_cred())
+
 /**
  * get_cred_many - Get references on a set of credentials
  * @cred: The credentials to reference
-- 
2.53.0