Merge patch series "cred: rework {override,revert}_creds()"

Christian Brauner <brauner@kernel.org> says:

For the v6.13 cycle we switched overlayfs to a variant of
override_creds() that doesn't take an extra reference. To this end I
suggested introducing {override,revert}_creds_light() which overlayfs
could use.

This seems to work rather well. This series follow Linus advice and
unifies the separate helpers and simply makes {override,revert}_creds()
do what {override,revert}_creds_light() currently does. Caller's that
really need the extra reference count can take it manually.

* patches from https://lore.kernel.org/r/20241125-work-cred-v2-0-68b9d38bb5b2@kernel.org: (29 commits)
  cred: remove unused get_new_cred()
  nfsd: avoid pointless cred reference count bump
  cachefiles: avoid pointless cred reference count bump
  dns_resolver: avoid pointless cred reference count bump
  trace: avoid pointless cred reference count bump
  cgroup: avoid pointless cred reference count bump
  acct: avoid pointless reference count bump
  io_uring: avoid pointless cred reference count bump
  smb: avoid pointless cred reference count bump
  cifs: avoid pointless cred reference count bump
  cifs: avoid pointless cred reference count bump
  ovl: avoid pointless cred reference count bump
  open: avoid pointless cred reference count bump
  nfsfh: avoid pointless cred reference count bump
  nfs/nfs4recover: avoid pointless cred reference count bump
  nfs/nfs4idmap: avoid pointless reference count bump
  nfs/localio: avoid pointless cred reference count bumps
  coredump: avoid pointless cred reference count bump
  binfmt_misc: avoid pointless cred reference count bump
  aio: avoid pointless cred reference count bump
  ...

Link: https://lore.kernel.org/r/20241125-work-cred-v2-0-68b9d38bb5b2@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 5 insertions, 21 deletions

diff --git a/include/linux/cred.h b/include/linux/cred.h
index e4a3155fe409..360f5fd3854b 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -155,8 +155,6 @@ extern struct cred *prepare_creds(void);
 extern struct cred *prepare_exec_creds(void);
 extern int commit_creds(struct cred *);
 extern void abort_creds(struct cred *);
-extern const struct cred *override_creds(const struct cred *);
-extern void revert_creds(const struct cred *);
 extern struct cred *prepare_kernel_cred(struct task_struct *);
 extern int set_security_override(struct cred *, u32);
 extern int set_security_override_from_ctx(struct cred *, const char *);
@@ -172,12 +170,7 @@ 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)
+static inline const struct cred *override_creds(const struct cred *override_cred)
 {
 	const struct cred *old = current->cred;
 
@@ -185,9 +178,12 @@ static inline const struct cred *override_creds_light(const struct cred *overrid
 	return old;
 }
 
-static inline void revert_creds_light(const struct cred *revert_cred)
+static inline const struct cred *revert_creds(const struct cred *revert_cred)
 {
+	const struct cred *override_cred = current->cred;
+
 	rcu_assign_pointer(current->cred, revert_cred);
+	return override_cred;
 }
 
 /**
@@ -205,18 +201,6 @@ static inline struct cred *get_new_cred_many(struct cred *cred, int nr)
 }
 
 /**
- * get_new_cred - Get a reference on a new set of credentials
- * @cred: The new credentials to reference
- *
- * Get a reference on the specified set of new credentials.  The caller must
- * release the reference.
- */
-static inline struct cred *get_new_cred(struct cred *cred)
-{
-	return get_new_cred_many(cred, 1);
-}
-
-/**
  * get_cred_many - Get references on a set of credentials
  * @cred: The credentials to reference
  * @nr: Number of references to acquire