umh: creds: kill subprocess_info->cred logic

Now that nobody ever changes subprocess_info->cred we can kill this member
and related code.  ____call_usermodehelper() always runs in the context of
freshly forked kernel thread, it has the proper ->cred copied from its
parent kthread, keventd.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/cred.h

@@ -156,7 +156,6 @@ extern int copy_creds(struct task_struct *, unsigned long);
 extern struct cred *cred_alloc_blank(void);
 extern struct cred *prepare_creds(void);
 extern struct cred *prepare_exec_creds(void);
-extern struct cred *prepare_usermodehelper_creds(void);
 extern int commit_creds(struct cred *);
 extern void abort_creds(struct cred *);
 extern const struct cred *override_creds(const struct cred *);

include/linux/kmod.h

@@ -56,7 +56,6 @@ enum umh_wait {
 struct subprocess_info {
 	struct work_struct work;
 	struct completion *complete;
-	struct cred *cred;
 	char *path;
 	char **argv;
 	char **envp;

kernel/cred.c

@@ -346,66 +346,6 @@ struct cred *prepare_exec_creds(void)
 	return new;
 }
 
-/*
- * prepare new credentials for the usermode helper dispatcher
- */
-struct cred *prepare_usermodehelper_creds(void)
-{
-#ifdef CONFIG_KEYS
-	struct thread_group_cred *tgcred = NULL;
-#endif
-	struct cred *new;
-
-#ifdef CONFIG_KEYS
-	tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
-	if (!tgcred)
-		return NULL;
-#endif
-
-	new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
-	if (!new)
-		goto free_tgcred;
-
-	kdebug("prepare_usermodehelper_creds() alloc %p", new);
-
-	memcpy(new, &init_cred, sizeof(struct cred));
-
-	atomic_set(&new->usage, 1);
-	set_cred_subscribers(new, 0);
-	get_group_info(new->group_info);
-	get_uid(new->user);
-
-#ifdef CONFIG_KEYS
-	new->thread_keyring = NULL;
-	new->request_key_auth = NULL;
-	new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
-
-	atomic_set(&tgcred->usage, 1);
-	spin_lock_init(&tgcred->lock);
-	new->tgcred = tgcred;
-#endif
-
-#ifdef CONFIG_SECURITY
-	new->security = NULL;
-#endif
-	if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
-		goto error;
-	validate_creds(new);
-
-	BUG_ON(atomic_read(&new->usage) != 1);
-	return new;
-
-error:
-	put_cred(new);
-	return NULL;
-
-free_tgcred:
-#ifdef CONFIG_KEYS
-	kfree(tgcred);
-#endif
-	return NULL;
-}
-
 /*
  * Copy credentials for the new process created by fork()
  *

kernel/kmod.c

@@ -134,8 +134,6 @@ static int ____call_usermodehelper(void *data)
 	struct subprocess_info *sub_info = data;
 	int retval;
 
-	BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
-
 	/* Unblock all signals */
 	spin_lock_irq(&current->sighand->siglock);
 	flush_signal_handlers(current, 1);
@@ -143,10 +141,6 @@ static int ____call_usermodehelper(void *data)
 	recalc_sigpending();
 	spin_unlock_irq(&current->sighand->siglock);
 
-	/* Install the credentials */
-	commit_creds(sub_info->cred);
-	sub_info->cred = NULL;
-
 	/* We can run anywhere, unlike our parent keventd(). */
 	set_cpus_allowed_ptr(current, cpu_all_mask);
 
@@ -174,8 +168,6 @@ void call_usermodehelper_freeinfo(struct subprocess_info *info)
 {
 	if (info->cleanup)
 		(*info->cleanup)(info);
-	if (info->cred)
-		put_cred(info->cred);
 	kfree(info);
 }
 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
@@ -231,8 +223,6 @@ static void __call_usermodehelper(struct work_struct *work)
 	pid_t pid;
 	enum umh_wait wait = sub_info->wait;
 
-	BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
-
 	/* CLONE_VFORK: wait until the usermode helper has execve'd
 	 * successfully We need the data structures to stay around
 	 * until that is done.  */
@@ -355,12 +345,6 @@ struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 	sub_info->path = path;
 	sub_info->argv = argv;
 	sub_info->envp = envp;
-	sub_info->cred = prepare_usermodehelper_creds();
-	if (!sub_info->cred) {
-		kfree(sub_info);
-		return NULL;
-	}
-
   out:
 	return sub_info;
 }
@@ -411,9 +395,6 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,
 	DECLARE_COMPLETION_ONSTACK(done);
 	int retval = 0;
 
-	BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
-	validate_creds(sub_info->cred);
-
 	helper_lock();
 	if (sub_info->path[0] == '\0')
 		goto out;