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SubjectRe: [PATCH 5/6] userns: Use refcount_t for reference counting instead atomic_t
On 2018-07-03 22:01:40 [+0200], To linux-kernel@vger.kernel.org wrote:
> 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.

Ingo, Andrew: who of you two feels most comfortable to apply this one
(and 6/6 of this series, both `userns')? If none, who would you suggest?

> Cc: Andrew Morton <akpm@linux-foundation.org>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> include/linux/sched/user.h | 5 +++--
> kernel/user.c | 8 ++++----
> 2 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
> index 96fe289c4c6e..39ad98c09c58 100644
> --- a/include/linux/sched/user.h
> +++ b/include/linux/sched/user.h
> @@ -4,6 +4,7 @@
>
> #include <linux/uidgid.h>
> #include <linux/atomic.h>
> +#include <linux/refcount.h>
> #include <linux/ratelimit.h>
>
> struct key;
> @@ -12,7 +13,7 @@ struct key;
> * 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
> @@ -59,7 +60,7 @@ extern struct user_struct root_user;
> 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 36288d840675..5f65ef195259 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -96,7 +96,7 @@ 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,
> @@ -123,7 +123,7 @@ 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;
> }
> }
> @@ -170,7 +170,7 @@ 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);
> @@ -191,7 +191,7 @@ struct user_struct *alloc_uid(kuid_t uid)
> goto out_unlock;
>
> new->uid = uid;
> - atomic_set(&new->__count, 1);
> + refcount_set(&new->__count, 1);
> ratelimit_state_init(&new->ratelimit, HZ, 100);
> ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
>
> --
> 2.18.0

Sebastian

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