[PATCH 03/19] kernel: convert user_struct.__count from atomic_t to refcount_t

refcount_t type and corresponding API should be used instead of atomic_t when the variable is used as a reference counter. This allows to avoid accidental refcounter overflows that might lead to use-after-free situations. Signed-off-by: Elena Reshetova <elena.reshetova(a)intel.com&gt; Signed-off-by: Hans Liljestrand <ishkamiel(a)gmail.com&gt; Signed-off-by: Kees Cook <keescook(a)chromium.org&gt; Signed-off-by: David Windsor <dwindsor(a)gmail.com&gt; --- include/linux/sched.h | 4 ++-- kernel/user.c | 8 ++++---- 2 files changed, 6 insertions(+), 6 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 6aad885..e90396f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -844,7 +844,7 @@ static inline int signal_group_exit(const struct signal_struct *sig) * Some day this will be a full-fledged user tracking system.. */ struct user_struct { - atomic_t __count; /* reference count */ + refcount_t __count; /* reference count */ atomic_t processes; /* How many processes does this user have? */ atomic_t sigpending; /* How many pending signals does this user have? */ #ifdef CONFIG_FANOTIFY @@ -2694,7 +2694,7 @@ extern struct task_struct *find_task_by_pid_ns(pid_t nr, extern struct user_struct * alloc_uid(kuid_t); static inline struct user_struct *get_uid(struct user_struct *u) { - atomic_inc(&u->__count); + refcount_inc(&u->__count); return u; } extern void free_uid(struct user_struct *); diff --git a/kernel/user.c b/kernel/user.c index b069ccb..d9dff8e 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -89,7 +89,7 @@ static DEFINE_SPINLOCK(uidhash_lock); /* root_user.__count is 1, for init task cred */ struct user_struct root_user = { - .__count = ATOMIC_INIT(1), + .__count = REFCOUNT_INIT(1), .processes = ATOMIC_INIT(1), .sigpending = ATOMIC_INIT(0), .locked_shm = 0, @@ -115,7 +115,7 @@ static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) hlist_for_each_entry(user, hashent, uidhash_node) { if (uid_eq(user->uid, uid)) { - atomic_inc(&user->__count); + refcount_inc(&user->__count); return user; } } @@ -162,7 +162,7 @@ void free_uid(struct user_struct *up) return; local_irq_save(flags); - if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) + if (refcount_dec_and_lock(&up->__count, &uidhash_lock)) free_user(up, flags); else local_irq_restore(flags); @@ -183,7 +183,7 @@ struct user_struct *alloc_uid(kuid_t uid) goto out_unlock; new->uid = uid; - atomic_set(&new->__count, 1); + refcount_set(&new->__count, 1); /* * Before adding this, check whether we raced -- 2.7.4