From: Alexey Gladkov <gladkov.alexey@gmail.com> To: LKML <linux-kernel@vger.kernel.org>, Kernel Hardening <kernel-hardening@lists.openwall.com>, Linux Containers <containers@lists.linux-foundation.org>, linux-mm@kvack.org Cc: Jens Axboe <axboe@kernel.dk>, Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>, Linus Torvalds <torvalds@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, "Eric W . Biederman" <ebiederm@xmission.com>, Andrew Morton <akpm@linux-foundation.org>, Alexey Gladkov <legion@kernel.org> Subject: [PATCH v9 3/8] Use atomic_t for ucounts reference counting Date: Tue, 23 Mar 2021 21:59:12 +0100 [thread overview] Message-ID: <54956fd06ab4a9938421f345ecf2e1518161cb38.1616533074.git.gladkov.alexey@gmail.com> (raw) In-Reply-To: <cover.1616533074.git.gladkov.alexey@gmail.com> The current implementation of the ucounts reference counter requires the use of spin_lock. We're going to use get_ucounts() in more performance critical areas like a handling of RLIMIT_SIGPENDING. Now we need to use spin_lock only if we want to change the hashtable. v9: * Use a negative value to check that the ucounts->count is close to overflow. Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com> --- include/linux/user_namespace.h | 4 +-- kernel/ucount.c | 53 ++++++++++++---------------------- 2 files changed, 21 insertions(+), 36 deletions(-) diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index f71b5a4a3e74..d84cc2c0b443 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -92,7 +92,7 @@ struct ucounts { struct hlist_node node; struct user_namespace *ns; kuid_t uid; - int count; + atomic_t count; atomic_long_t ucount[UCOUNT_COUNTS]; }; @@ -104,7 +104,7 @@ void retire_userns_sysctls(struct user_namespace *ns); struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type); void dec_ucount(struct ucounts *ucounts, enum ucount_type type); struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid); -struct ucounts *get_ucounts(struct ucounts *ucounts); +struct ucounts * __must_check get_ucounts(struct ucounts *ucounts); void put_ucounts(struct ucounts *ucounts); #ifdef CONFIG_USER_NS diff --git a/kernel/ucount.c b/kernel/ucount.c index 50cc1dfb7d28..7bac19bb3f1e 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -11,7 +11,7 @@ struct ucounts init_ucounts = { .ns = &init_user_ns, .uid = GLOBAL_ROOT_UID, - .count = 1, + .count = ATOMIC_INIT(1), }; #define UCOUNTS_HASHTABLE_BITS 10 @@ -139,6 +139,15 @@ static void hlist_add_ucounts(struct ucounts *ucounts) spin_unlock_irq(&ucounts_lock); } +struct ucounts *get_ucounts(struct ucounts *ucounts) +{ + if (ucounts && atomic_add_negative(1, &ucounts->count)) { + atomic_dec(&ucounts->count); + ucounts = NULL; + } + return ucounts; +} + struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) { struct hlist_head *hashent = ucounts_hashentry(ns, uid); @@ -155,7 +164,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) new->ns = ns; new->uid = uid; - new->count = 0; + atomic_set(&new->count, 1); spin_lock_irq(&ucounts_lock); ucounts = find_ucounts(ns, uid, hashent); @@ -163,33 +172,12 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) kfree(new); } else { hlist_add_head(&new->node, hashent); - ucounts = new; + spin_unlock_irq(&ucounts_lock); + return new; } } - if (ucounts->count == INT_MAX) - ucounts = NULL; - else - ucounts->count += 1; spin_unlock_irq(&ucounts_lock); - return ucounts; -} - -struct ucounts *get_ucounts(struct ucounts *ucounts) -{ - unsigned long flags; - - if (!ucounts) - return NULL; - - spin_lock_irqsave(&ucounts_lock, flags); - if (ucounts->count == INT_MAX) { - WARN_ONCE(1, "ucounts: counter has reached its maximum value"); - ucounts = NULL; - } else { - ucounts->count += 1; - } - spin_unlock_irqrestore(&ucounts_lock, flags); - + ucounts = get_ucounts(ucounts); return ucounts; } @@ -197,15 +185,12 @@ void put_ucounts(struct ucounts *ucounts) { unsigned long flags; - spin_lock_irqsave(&ucounts_lock, flags); - ucounts->count -= 1; - if (!ucounts->count) + if (atomic_dec_and_test(&ucounts->count)) { + spin_lock_irqsave(&ucounts_lock, flags); hlist_del_init(&ucounts->node); - else - ucounts = NULL; - spin_unlock_irqrestore(&ucounts_lock, flags); - - kfree(ucounts); + spin_unlock_irqrestore(&ucounts_lock, flags); + kfree(ucounts); + } } static inline bool atomic_long_inc_below(atomic_long_t *v, int u) -- 2.29.3 _______________________________________________ Containers mailing list Containers@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/containers
WARNING: multiple messages have this Message-ID (diff)
From: Alexey Gladkov <gladkov.alexey@gmail.com> To: LKML <linux-kernel@vger.kernel.org>, Kernel Hardening <kernel-hardening@lists.openwall.com>, Linux Containers <containers@lists.linux-foundation.org>, linux-mm@kvack.org Cc: Alexey Gladkov <legion@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Christian Brauner <christian.brauner@ubuntu.com>, "Eric W . Biederman" <ebiederm@xmission.com>, Jann Horn <jannh@google.com>, Jens Axboe <axboe@kernel.dk>, Kees Cook <keescook@chromium.org>, Linus Torvalds <torvalds@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com> Subject: [PATCH v9 3/8] Use atomic_t for ucounts reference counting Date: Tue, 23 Mar 2021 21:59:12 +0100 [thread overview] Message-ID: <54956fd06ab4a9938421f345ecf2e1518161cb38.1616533074.git.gladkov.alexey@gmail.com> (raw) In-Reply-To: <cover.1616533074.git.gladkov.alexey@gmail.com> The current implementation of the ucounts reference counter requires the use of spin_lock. We're going to use get_ucounts() in more performance critical areas like a handling of RLIMIT_SIGPENDING. Now we need to use spin_lock only if we want to change the hashtable. v9: * Use a negative value to check that the ucounts->count is close to overflow. Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com> --- include/linux/user_namespace.h | 4 +-- kernel/ucount.c | 53 ++++++++++++---------------------- 2 files changed, 21 insertions(+), 36 deletions(-) diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index f71b5a4a3e74..d84cc2c0b443 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -92,7 +92,7 @@ struct ucounts { struct hlist_node node; struct user_namespace *ns; kuid_t uid; - int count; + atomic_t count; atomic_long_t ucount[UCOUNT_COUNTS]; }; @@ -104,7 +104,7 @@ void retire_userns_sysctls(struct user_namespace *ns); struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type); void dec_ucount(struct ucounts *ucounts, enum ucount_type type); struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid); -struct ucounts *get_ucounts(struct ucounts *ucounts); +struct ucounts * __must_check get_ucounts(struct ucounts *ucounts); void put_ucounts(struct ucounts *ucounts); #ifdef CONFIG_USER_NS diff --git a/kernel/ucount.c b/kernel/ucount.c index 50cc1dfb7d28..7bac19bb3f1e 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -11,7 +11,7 @@ struct ucounts init_ucounts = { .ns = &init_user_ns, .uid = GLOBAL_ROOT_UID, - .count = 1, + .count = ATOMIC_INIT(1), }; #define UCOUNTS_HASHTABLE_BITS 10 @@ -139,6 +139,15 @@ static void hlist_add_ucounts(struct ucounts *ucounts) spin_unlock_irq(&ucounts_lock); } +struct ucounts *get_ucounts(struct ucounts *ucounts) +{ + if (ucounts && atomic_add_negative(1, &ucounts->count)) { + atomic_dec(&ucounts->count); + ucounts = NULL; + } + return ucounts; +} + struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) { struct hlist_head *hashent = ucounts_hashentry(ns, uid); @@ -155,7 +164,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) new->ns = ns; new->uid = uid; - new->count = 0; + atomic_set(&new->count, 1); spin_lock_irq(&ucounts_lock); ucounts = find_ucounts(ns, uid, hashent); @@ -163,33 +172,12 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) kfree(new); } else { hlist_add_head(&new->node, hashent); - ucounts = new; + spin_unlock_irq(&ucounts_lock); + return new; } } - if (ucounts->count == INT_MAX) - ucounts = NULL; - else - ucounts->count += 1; spin_unlock_irq(&ucounts_lock); - return ucounts; -} - -struct ucounts *get_ucounts(struct ucounts *ucounts) -{ - unsigned long flags; - - if (!ucounts) - return NULL; - - spin_lock_irqsave(&ucounts_lock, flags); - if (ucounts->count == INT_MAX) { - WARN_ONCE(1, "ucounts: counter has reached its maximum value"); - ucounts = NULL; - } else { - ucounts->count += 1; - } - spin_unlock_irqrestore(&ucounts_lock, flags); - + ucounts = get_ucounts(ucounts); return ucounts; } @@ -197,15 +185,12 @@ void put_ucounts(struct ucounts *ucounts) { unsigned long flags; - spin_lock_irqsave(&ucounts_lock, flags); - ucounts->count -= 1; - if (!ucounts->count) + if (atomic_dec_and_test(&ucounts->count)) { + spin_lock_irqsave(&ucounts_lock, flags); hlist_del_init(&ucounts->node); - else - ucounts = NULL; - spin_unlock_irqrestore(&ucounts_lock, flags); - - kfree(ucounts); + spin_unlock_irqrestore(&ucounts_lock, flags); + kfree(ucounts); + } } static inline bool atomic_long_inc_below(atomic_long_t *v, int u) -- 2.29.3
next prev parent reply other threads:[~2021-03-23 21:00 UTC|newest] Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov 2021-03-23 20:59 ` [PATCH v9 1/8] Increase size of ucounts to atomic_long_t Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov 2021-03-23 20:59 ` [PATCH v9 2/8] Add a reference to ucounts for each cred Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov [this message] 2021-03-23 20:59 ` [PATCH v9 3/8] Use atomic_t for ucounts reference counting Alexey Gladkov 2021-04-05 17:01 ` Eric W. Biederman 2021-04-05 17:01 ` Eric W. Biederman 2021-04-05 17:01 ` Eric W. Biederman 2021-03-23 20:59 ` [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov 2021-04-05 16:56 ` Eric W. Biederman 2021-04-05 16:56 ` Eric W. Biederman 2021-04-05 16:56 ` Eric W. Biederman 2021-04-06 15:44 ` Alexey Gladkov 2021-04-06 15:44 ` Alexey Gladkov 2021-04-07 16:56 ` Eric W. Biederman 2021-04-07 16:56 ` Eric W. Biederman 2021-04-07 16:56 ` Eric W. Biederman 2021-03-23 20:59 ` [PATCH v9 5/8] Reimplement RLIMIT_MSGQUEUE " Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov 2021-03-23 20:59 ` [PATCH v9 6/8] Reimplement RLIMIT_SIGPENDING " Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov 2021-04-05 16:58 ` Eric W. Biederman 2021-04-05 16:58 ` Eric W. Biederman 2021-04-05 16:58 ` Eric W. Biederman 2021-03-23 20:59 ` [PATCH v9 7/8] Reimplement RLIMIT_MEMLOCK " Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov 2021-03-23 20:59 ` [PATCH v9 8/8] kselftests: Add test to check for rlimit changes in different user namespaces Alexey Gladkov 2021-03-23 20:59 ` Alexey Gladkov 2021-04-05 17:03 ` [PATCH v9 0/8] Count rlimits in each user namespace Eric W. Biederman 2021-04-05 17:03 ` Eric W. Biederman 2021-04-05 17:03 ` Eric W. Biederman
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