cred: switch to using atomic_long_t

There are multiple ways to grab references to credentials, and the only
protection we have against overflowing it is the memory required to do
so.

With memory sizes only moving in one direction, let's bump the reference
count to 64-bit and move it outside the realm of feasibly overflowing.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: axboe

include/linux/cred.h

@@ -109,7 +109,7 @@ static inline int groups_search(const struct group_info *group_info, kgid_t grp)
  * same context as task->real_cred.
  */
 struct cred {
-	atomic_t	usage;
+	atomic_long_t	usage;
 #ifdef CONFIG_DEBUG_CREDENTIALS
 	atomic_t	subscribers;	/* number of processes subscribed */
 	void		*put_addr;
@@ -229,7 +229,7 @@ static inline bool cap_ambient_invariant_ok(const struct cred *cred)
  */
 static inline struct cred *get_new_cred_many(struct cred *cred, int nr)
 {
-	atomic_add(nr, &cred->usage);
+	atomic_long_add(nr, &cred->usage);
 	return cred;
 }
 
@@ -288,7 +288,7 @@ static inline const struct cred *get_cred_rcu(const struct cred *cred)
 	struct cred *nonconst_cred = (struct cred *) cred;
 	if (!cred)
 		return NULL;
-	if (!atomic_inc_not_zero(&nonconst_cred->usage))
+	if (!atomic_long_inc_not_zero(&nonconst_cred->usage))
 		return NULL;
 	validate_creds(cred);
 	nonconst_cred->non_rcu = 0;
@@ -313,7 +313,7 @@ static inline void put_cred_many(const struct cred *_cred, int nr)
 
 	if (cred) {
 		validate_creds(cred);
-		if (atomic_sub_and_test(nr, &cred->usage))
+		if (atomic_long_sub_and_test(nr, &cred->usage))
 			__put_cred(cred);
 	}
 }

kernel/cred.c

@@ -102,17 +102,17 @@ static void put_cred_rcu(struct rcu_head *rcu)
 
 #ifdef CONFIG_DEBUG_CREDENTIALS
 	if (cred->magic != CRED_MAGIC_DEAD ||
-	    atomic_read(&cred->usage) != 0 ||
+	    atomic_long_read(&cred->usage) != 0 ||
 	    read_cred_subscribers(cred) != 0)
 		panic("CRED: put_cred_rcu() sees %p with"
-		      " mag %x, put %p, usage %d, subscr %d\n",
+		      " mag %x, put %p, usage %ld, subscr %d\n",
 		      cred, cred->magic, cred->put_addr,
-		      atomic_read(&cred->usage),
+		      atomic_long_read(&cred->usage),
 		      read_cred_subscribers(cred));
 #else
-	if (atomic_read(&cred->usage) != 0)
-		panic("CRED: put_cred_rcu() sees %p with usage %d\n",
-		      cred, atomic_read(&cred->usage));
+	if (atomic_long_read(&cred->usage) != 0)
+		panic("CRED: put_cred_rcu() sees %p with usage %ld\n",
+		      cred, atomic_long_read(&cred->usage));
 #endif
 
 	security_cred_free(cred);
@@ -137,11 +137,11 @@ static void put_cred_rcu(struct rcu_head *rcu)
  */
 void __put_cred(struct cred *cred)
 {
-	kdebug("__put_cred(%p{%d,%d})", cred,
-	       atomic_read(&cred->usage),
+	kdebug("__put_cred(%p{%ld,%d})", cred,
+	       atomic_long_read(&cred->usage),
 	       read_cred_subscribers(cred));
 
-	BUG_ON(atomic_read(&cred->usage) != 0);
+	BUG_ON(atomic_long_read(&cred->usage) != 0);
 #ifdef CONFIG_DEBUG_CREDENTIALS
 	BUG_ON(read_cred_subscribers(cred) != 0);
 	cred->magic = CRED_MAGIC_DEAD;
@@ -164,8 +164,8 @@ void exit_creds(struct task_struct *tsk)
 {
 	struct cred *real_cred, *cred;
 
-	kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
-	       atomic_read(&tsk->cred->usage),
+	kdebug("exit_creds(%u,%p,%p,{%ld,%d})", tsk->pid, tsk->real_cred, tsk->cred,
+	       atomic_long_read(&tsk->cred->usage),
 	       read_cred_subscribers(tsk->cred));
 
 	real_cred = (struct cred *) tsk->real_cred;
@@ -230,7 +230,7 @@ struct cred *cred_alloc_blank(void)
 	if (!new)
 		return NULL;
 
-	atomic_set(&new->usage, 1);
+	atomic_long_set(&new->usage, 1);
 #ifdef CONFIG_DEBUG_CREDENTIALS
 	new->magic = CRED_MAGIC;
 #endif
@@ -276,7 +276,7 @@ struct cred *prepare_creds(void)
 	memcpy(new, old, sizeof(struct cred));
 
 	new->non_rcu = 0;
-	atomic_set(&new->usage, 1);
+	atomic_long_set(&new->usage, 1);
 	set_cred_subscribers(new, 0);
 	get_group_info(new->group_info);
 	get_uid(new->user);
@@ -363,8 +363,8 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 	    ) {
 		p->real_cred = get_cred_many(p->cred, 2);
 		alter_cred_subscribers(p->cred, 2);
-		kdebug("share_creds(%p{%d,%d})",
-		       p->cred, atomic_read(&p->cred->usage),
+		kdebug("share_creds(%p{%ld,%d})",
+		       p->cred, atomic_long_read(&p->cred->usage),
 		       read_cred_subscribers(p->cred));
 		inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 		return 0;
@@ -457,8 +457,8 @@ int commit_creds(struct cred *new)
 	struct task_struct *task = current;
 	const struct cred *old = task->real_cred;
 
-	kdebug("commit_creds(%p{%d,%d})", new,
-	       atomic_read(&new->usage),
+	kdebug("commit_creds(%p{%ld,%d})", new,
+	       atomic_long_read(&new->usage),
 	       read_cred_subscribers(new));
 
 	BUG_ON(task->cred != old);
@@ -467,7 +467,7 @@ int commit_creds(struct cred *new)
 	validate_creds(old);
 	validate_creds(new);
 #endif
-	BUG_ON(atomic_read(&new->usage) < 1);
+	BUG_ON(atomic_long_read(&new->usage) < 1);
 
 	get_cred(new); /* we will require a ref for the subj creds too */
 
@@ -539,14 +539,14 @@ EXPORT_SYMBOL(commit_creds);
  */
 void abort_creds(struct cred *new)
 {
-	kdebug("abort_creds(%p{%d,%d})", new,
-	       atomic_read(&new->usage),
+	kdebug("abort_creds(%p{%ld,%d})", new,
+	       atomic_long_read(&new->usage),
 	       read_cred_subscribers(new));
 
 #ifdef CONFIG_DEBUG_CREDENTIALS
 	BUG_ON(read_cred_subscribers(new) != 0);
 #endif
-	BUG_ON(atomic_read(&new->usage) < 1);
+	BUG_ON(atomic_long_read(&new->usage) < 1);
 	put_cred(new);
 }
 EXPORT_SYMBOL(abort_creds);
@@ -562,8 +562,8 @@ const struct cred *override_creds(const struct cred *new)
 {
 	const struct cred *old = current->cred;
 
-	kdebug("override_creds(%p{%d,%d})", new,
-	       atomic_read(&new->usage),
+	kdebug("override_creds(%p{%ld,%d})", new,
+	       atomic_long_read(&new->usage),
 	       read_cred_subscribers(new));
 
 	validate_creds(old);
@@ -585,8 +585,8 @@ const struct cred *override_creds(const struct cred *new)
 	rcu_assign_pointer(current->cred, new);
 	alter_cred_subscribers(old, -1);
 
-	kdebug("override_creds() = %p{%d,%d}", old,
-	       atomic_read(&old->usage),
+	kdebug("override_creds() = %p{%ld,%d}", old,
+	       atomic_long_read(&old->usage),
 	       read_cred_subscribers(old));
 	return old;
 }
@@ -603,8 +603,8 @@ void revert_creds(const struct cred *old)
 {
 	const struct cred *override = current->cred;
 
-	kdebug("revert_creds(%p{%d,%d})", old,
-	       atomic_read(&old->usage),
+	kdebug("revert_creds(%p{%ld,%d})", old,
+	       atomic_long_read(&old->usage),
 	       read_cred_subscribers(old));
 
 	validate_creds(old);
@@ -735,7 +735,7 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
 
 	*new = *old;
 	new->non_rcu = 0;
-	atomic_set(&new->usage, 1);
+	atomic_long_set(&new->usage, 1);
 	set_cred_subscribers(new, 0);
 	get_uid(new->user);
 	get_user_ns(new->user_ns);
@@ -849,8 +849,8 @@ static void dump_invalid_creds(const struct cred *cred, const char *label,
 	       cred == tsk->cred ? "[eff]" : "");
 	pr_err("->magic=%x, put_addr=%p\n",
 	       cred->magic, cred->put_addr);
-	pr_err("->usage=%d, subscr=%d\n",
-	       atomic_read(&cred->usage),
+	pr_err("->usage=%ld, subscr=%d\n",
+	       atomic_long_read(&cred->usage),
 	       read_cred_subscribers(cred));
 	pr_err("->*uid = { %d,%d,%d,%d }\n",
 		from_kuid_munged(&init_user_ns, cred->uid),
@@ -922,9 +922,9 @@ EXPORT_SYMBOL(__validate_process_creds);
  */
 void validate_creds_for_do_exit(struct task_struct *tsk)
 {
-	kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
+	kdebug("validate_creds_for_do_exit(%p,%p{%ld,%d})",
 	       tsk->real_cred, tsk->cred,
-	       atomic_read(&tsk->cred->usage),
+	       atomic_long_read(&tsk->cred->usage),
 	       read_cred_subscribers(tsk->cred));
 
 	__validate_process_creds(tsk, __FILE__, __LINE__);