cred: get rid of CONFIG_DEBUG_CREDENTIALS

This code is rarely (never?) enabled by distros, and it hasn't caught
anything in decades. Let's kill off this legacy debug code.
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/configs/skiroot_defconfig

@@ -301,7 +301,6 @@ CONFIG_WQ_WATCHDOG=y
 CONFIG_DEBUG_SG=y
 CONFIG_DEBUG_NOTIFIERS=y
 CONFIG_BUG_ON_DATA_CORRUPTION=y
-CONFIG_DEBUG_CREDENTIALS=y
 # CONFIG_FTRACE is not set
 CONFIG_XMON=y
 # CONFIG_RUNTIME_TESTING_MENU is not set

arch/s390/configs/debug_defconfig

@@ -834,7 +834,6 @@ CONFIG_DEBUG_IRQFLAGS=y
 CONFIG_DEBUG_LIST=y
 CONFIG_DEBUG_SG=y
 CONFIG_DEBUG_NOTIFIERS=y
-CONFIG_DEBUG_CREDENTIALS=y
 CONFIG_RCU_TORTURE_TEST=m
 CONFIG_RCU_REF_SCALE_TEST=m
 CONFIG_RCU_CPU_STALL_TIMEOUT=300

fs/nfsd/auth.c

@@ -26,8 +26,6 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
 	int i;
 	int flags = nfsexp_flags(rqstp, exp);
 
-	validate_process_creds();
-
 	/* discard any old override before preparing the new set */
 	revert_creds(get_cred(current_real_cred()));
 	new = prepare_creds();
@@ -81,10 +79,8 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
 	else
 		new->cap_effective = cap_raise_nfsd_set(new->cap_effective,
 							new->cap_permitted);
-	validate_process_creds();
 	put_cred(override_creds(new));
 	put_cred(new);
-	validate_process_creds();
 	return 0;
 
 oom:

fs/nfsd/nfssvc.c

@@ -955,7 +955,6 @@ nfsd(void *vrqstp)
 		rqstp->rq_server->sv_maxconn = nn->max_connections;
 
 		svc_recv(rqstp);
-		validate_process_creds();
 	}
 
 	atomic_dec(&nfsdstats.th_cnt);

fs/nfsd/vfs.c

@@ -901,7 +901,6 @@ nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type,
 	int host_err;
 	bool retried = false;
 
-	validate_process_creds();
 	/*
 	 * If we get here, then the client has already done an "open",
 	 * and (hopefully) checked permission - so allow OWNER_OVERRIDE
@@ -926,7 +925,6 @@ nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type,
 		}
 		err = nfserrno(host_err);
 	}
-	validate_process_creds();
 	return err;
 }
 
@@ -943,12 +941,7 @@ int
 nfsd_open_verified(struct svc_rqst *rqstp, struct svc_fh *fhp, int may_flags,
 		   struct file **filp)
 {
-	int err;
-
-	validate_process_creds();
-	err = __nfsd_open(rqstp, fhp, S_IFREG, may_flags, filp);
-	validate_process_creds();
-	return err;
+	return __nfsd_open(rqstp, fhp, S_IFREG, may_flags, filp);
 }
 
 /*

fs/open.c

@@ -1088,8 +1088,6 @@ struct file *dentry_open(const struct path *path, int flags,
 	int error;
 	struct file *f;
 
-	validate_creds(cred);
-
 	/* We must always pass in a valid mount pointer. */
 	BUG_ON(!path->mnt);
 
@@ -1128,7 +1126,6 @@ struct file *dentry_create(const struct path *path, int flags, umode_t mode,
 	struct file *f;
 	int error;
 
-	validate_creds(cred);
 	f = alloc_empty_file(flags, cred);
 	if (IS_ERR(f))
 		return f;

include/linux/cred.h

@@ -110,13 +110,6 @@ static inline int groups_search(const struct group_info *group_info, kgid_t grp)
  */
 struct cred {
 	atomic_long_t	usage;
-#ifdef CONFIG_DEBUG_CREDENTIALS
-	atomic_t	subscribers;	/* number of processes subscribed */
-	void		*put_addr;
-	unsigned	magic;
-#define CRED_MAGIC	0x43736564
-#define CRED_MAGIC_DEAD	0x44656144
-#endif
 	kuid_t		uid;		/* real UID of the task */
 	kgid_t		gid;		/* real GID of the task */
 	kuid_t		suid;		/* saved UID of the task */
@@ -172,46 +165,6 @@ extern int cred_fscmp(const struct cred *, const struct cred *);
 extern void __init cred_init(void);
 extern int set_cred_ucounts(struct cred *);
 
-/*
- * check for validity of credentials
- */
-#ifdef CONFIG_DEBUG_CREDENTIALS
-extern void __noreturn __invalid_creds(const struct cred *, const char *, unsigned);
-extern void __validate_process_creds(struct task_struct *,
-				     const char *, unsigned);
-
-extern bool creds_are_invalid(const struct cred *cred);
-
-static inline void __validate_creds(const struct cred *cred,
-				    const char *file, unsigned line)
-{
-	if (unlikely(creds_are_invalid(cred)))
-		__invalid_creds(cred, file, line);
-}
-
-#define validate_creds(cred)				\
-do {							\
-	__validate_creds((cred), __FILE__, __LINE__);	\
-} while(0)
-
-#define validate_process_creds()				\
-do {								\
-	__validate_process_creds(current, __FILE__, __LINE__);	\
-} while(0)
-
-extern void validate_creds_for_do_exit(struct task_struct *);
-#else
-static inline void validate_creds(const struct cred *cred)
-{
-}
-static inline void validate_creds_for_do_exit(struct task_struct *tsk)
-{
-}
-static inline void validate_process_creds(void)
-{
-}
-#endif
-
 static inline bool cap_ambient_invariant_ok(const struct cred *cred)
 {
 	return cap_issubset(cred->cap_ambient,
@@ -264,7 +217,6 @@ static inline const struct cred *get_cred_many(const struct cred *cred, int nr)
 	struct cred *nonconst_cred = (struct cred *) cred;
 	if (!cred)
 		return cred;
-	validate_creds(cred);
 	nonconst_cred->non_rcu = 0;
 	return get_new_cred_many(nonconst_cred, nr);
 }
@@ -290,7 +242,6 @@ static inline const struct cred *get_cred_rcu(const struct cred *cred)
 		return NULL;
 	if (!atomic_long_inc_not_zero(&nonconst_cred->usage))
 		return NULL;
-	validate_creds(cred);
 	nonconst_cred->non_rcu = 0;
 	return cred;
 }
@@ -312,7 +263,6 @@ static inline void put_cred_many(const struct cred *_cred, int nr)
 	struct cred *cred = (struct cred *) _cred;
 
 	if (cred) {
-		validate_creds(cred);
 		if (atomic_long_sub_and_test(nr, &cred->usage))
 			__put_cred(cred);
 	}

kernel/exit.c

@@ -824,8 +824,6 @@ void __noreturn do_exit(long code)
 	ptrace_event(PTRACE_EVENT_EXIT, code);
 	user_events_exit(tsk);
 
-	validate_creds_for_do_exit(tsk);
-
 	io_uring_files_cancel();
 	exit_signals(tsk);  /* sets PF_EXITING */
 
@@ -909,7 +907,6 @@ void __noreturn do_exit(long code)
 	if (tsk->task_frag.page)
 		put_page(tsk->task_frag.page);
 
-	validate_creds_for_do_exit(tsk);
 	exit_task_stack_account(tsk);
 
 	check_stack_usage();

lib/Kconfig.debug

@@ -1739,21 +1739,6 @@ config DEBUG_MAPLE_TREE
 
 endmenu
 
-config DEBUG_CREDENTIALS
-	bool "Debug credential management"
-	depends on DEBUG_KERNEL
-	help
-	  Enable this to turn on some debug checking for credential
-	  management.  The additional code keeps track of the number of
-	  pointers from task_structs to any given cred struct, and checks to
-	  see that this number never exceeds the usage count of the cred
-	  struct.
-
-	  Furthermore, if SELinux is enabled, this also checks that the
-	  security pointer in the cred struct is never seen to be invalid.
-
-	  If unsure, say N.
-
 source "kernel/rcu/Kconfig.debug"
 
 config DEBUG_WQ_FORCE_RR_CPU

net/sunrpc/auth.c

@@ -40,9 +40,6 @@ static unsigned long number_cred_unused;
 
 static struct cred machine_cred = {
 	.usage = ATOMIC_INIT(1),
-#ifdef CONFIG_DEBUG_CREDENTIALS
-	.magic = CRED_MAGIC,
-#endif
 };
 
 /*

security/selinux/hooks.c

@@ -1660,8 +1660,6 @@ static int inode_has_perm(const struct cred *cred,
 	struct inode_security_struct *isec;
 	u32 sid;
 
-	validate_creds(cred);
-
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
 
@@ -3056,8 +3054,6 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
 	struct inode_security_struct *isec;
 	u32 sid;
 
-	validate_creds(cred);
-
 	ad.type = LSM_AUDIT_DATA_DENTRY;
 	ad.u.dentry = dentry;
 	sid = cred_sid(cred);
@@ -3101,8 +3097,6 @@ static int selinux_inode_permission(struct inode *inode, int mask)
 	if (!mask)
 		return 0;
 
-	validate_creds(cred);
-
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
 

tools/objtool/noreturns.h

@@ -6,7 +6,6 @@
  *
  * Yes, this is unfortunate.  A better solution is in the works.
  */
-NORETURN(__invalid_creds)
 NORETURN(__kunit_abort)
 NORETURN(__module_put_and_kthread_exit)
 NORETURN(__reiserfs_panic)

tools/testing/selftests/bpf/config.x86_64

@@ -50,7 +50,6 @@ CONFIG_CRYPTO_SEQIV=y
 CONFIG_CRYPTO_XXHASH=y
 CONFIG_DCB=y
 CONFIG_DEBUG_ATOMIC_SLEEP=y
-CONFIG_DEBUG_CREDENTIALS=y
 CONFIG_DEBUG_INFO_BTF=y
 CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
 CONFIG_DEBUG_MEMORY_INIT=y

tools/testing/selftests/hid/config.common

@@ -46,7 +46,6 @@ CONFIG_CRYPTO_SEQIV=y
 CONFIG_CRYPTO_XXHASH=y
 CONFIG_DCB=y
 CONFIG_DEBUG_ATOMIC_SLEEP=y
-CONFIG_DEBUG_CREDENTIALS=y
 CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
 CONFIG_DEBUG_MEMORY_INIT=y
 CONFIG_DEFAULT_FQ_CODEL=y