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    Subject[PATCH v4 1/7] Add a reference to ucounts for each cred
    Date
    For RLIMIT_NPROC and some other rlimits the user_struct that holds the
    global limit is kept alive for the lifetime of a process by keeping it
    in struct cred. Add a ucounts reference to struct cred, so that
    RLIMIT_NPROC can switch from using a per user limit to using a per user
    per user namespace limit.

    Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
    ---
    include/linux/cred.h | 1 +
    include/linux/user_namespace.h | 7 ++++--
    kernel/cred.c | 20 +++++++++++++--
    kernel/ucount.c | 46 ++++++++++++++++++++++++++--------
    kernel/user_namespace.c | 1 +
    5 files changed, 61 insertions(+), 14 deletions(-)

    diff --git a/include/linux/cred.h b/include/linux/cred.h
    index 18639c069263..307744fcc387 100644
    --- a/include/linux/cred.h
    +++ b/include/linux/cred.h
    @@ -144,6 +144,7 @@ struct cred {
    #endif
    struct user_struct *user; /* real user ID subscription */
    struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */
    + struct ucounts *ucounts;
    struct group_info *group_info; /* supplementary groups for euid/fsgid */
    /* RCU deletion */
    union {
    diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
    index 64cf8ebdc4ec..4cf93f9f93a6 100644
    --- a/include/linux/user_namespace.h
    +++ b/include/linux/user_namespace.h
    @@ -85,7 +85,7 @@ struct user_namespace {
    struct ctl_table_header *sysctls;
    #endif
    struct ucounts *ucounts;
    - int ucount_max[UCOUNT_COUNTS];
    + long ucount_max[UCOUNT_COUNTS];
    } __randomize_layout;

    struct ucounts {
    @@ -93,7 +93,7 @@ struct ucounts {
    struct user_namespace *ns;
    kuid_t uid;
    int count;
    - atomic_t ucount[UCOUNT_COUNTS];
    + atomic_long_t ucount[UCOUNT_COUNTS];
    };

    extern struct user_namespace init_user_ns;
    @@ -102,6 +102,9 @@ bool setup_userns_sysctls(struct user_namespace *ns);
    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 *get_ucounts(struct ucounts *ucounts);
    +void put_ucounts(struct ucounts *ucounts);
    +void set_cred_ucounts(struct cred *cred, struct user_namespace *ns, kuid_t uid);

    #ifdef CONFIG_USER_NS

    diff --git a/kernel/cred.c b/kernel/cred.c
    index 421b1149c651..9473e71e784c 100644
    --- a/kernel/cred.c
    +++ b/kernel/cred.c
    @@ -119,6 +119,8 @@ static void put_cred_rcu(struct rcu_head *rcu)
    if (cred->group_info)
    put_group_info(cred->group_info);
    free_uid(cred->user);
    + if (cred->ucounts)
    + put_ucounts(cred->ucounts);
    put_user_ns(cred->user_ns);
    kmem_cache_free(cred_jar, cred);
    }
    @@ -144,6 +146,9 @@ void __put_cred(struct cred *cred)
    BUG_ON(cred == current->cred);
    BUG_ON(cred == current->real_cred);

    + if (cred->ucounts)
    + BUG_ON(cred->ucounts->ns != cred->user_ns);
    +
    if (cred->non_rcu)
    put_cred_rcu(&cred->rcu);
    else
    @@ -270,6 +275,7 @@ struct cred *prepare_creds(void)
    get_group_info(new->group_info);
    get_uid(new->user);
    get_user_ns(new->user_ns);
    + get_ucounts(new->ucounts);

    #ifdef CONFIG_KEYS
    key_get(new->session_keyring);
    @@ -363,6 +369,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
    ret = create_user_ns(new);
    if (ret < 0)
    goto error_put;
    + set_cred_ucounts(new, new->user_ns, new->euid);
    }

    #ifdef CONFIG_KEYS
    @@ -485,8 +492,11 @@ int commit_creds(struct cred *new)
    * in set_user().
    */
    alter_cred_subscribers(new, 2);
    - if (new->user != old->user)
    - atomic_inc(&new->user->processes);
    + if (new->user != old->user || new->user_ns != old->user_ns) {
    + if (new->user != old->user)
    + atomic_inc(&new->user->processes);
    + set_cred_ucounts(new, new->user_ns, new->euid);
    + }
    rcu_assign_pointer(task->real_cred, new);
    rcu_assign_pointer(task->cred, new);
    if (new->user != old->user)
    @@ -661,6 +671,11 @@ void __init cred_init(void)
    /* allocate a slab in which we can store credentials */
    cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0,
    SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
    + /*
    + * This is needed here because this is the first cred and there is no
    + * ucount reference to copy.
    + */
    + set_cred_ucounts(&init_cred, &init_user_ns, GLOBAL_ROOT_UID);
    }

    /**
    @@ -704,6 +719,7 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
    get_uid(new->user);
    get_user_ns(new->user_ns);
    get_group_info(new->group_info);
    + get_ucounts(new->ucounts);

    #ifdef CONFIG_KEYS
    new->session_keyring = NULL;
    diff --git a/kernel/ucount.c b/kernel/ucount.c
    index 11b1596e2542..8d3cf7369ee7 100644
    --- a/kernel/ucount.c
    +++ b/kernel/ucount.c
    @@ -125,7 +125,7 @@ static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struc
    return NULL;
    }

    -static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
    +static struct ucounts *__get_ucounts(struct user_namespace *ns, kuid_t uid)
    {
    struct hlist_head *hashent = ucounts_hashentry(ns, uid);
    struct ucounts *ucounts, *new;
    @@ -160,7 +160,7 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
    return ucounts;
    }

    -static void put_ucounts(struct ucounts *ucounts)
    +void put_ucounts(struct ucounts *ucounts)
    {
    unsigned long flags;

    @@ -175,14 +175,40 @@ static void put_ucounts(struct ucounts *ucounts)
    kfree(ucounts);
    }

    -static inline bool atomic_inc_below(atomic_t *v, int u)
    +struct ucounts *get_ucounts(struct ucounts *ucounts)
    {
    - int c, old;
    - c = atomic_read(v);
    + unsigned long flags;
    +
    + if (ucounts) {
    + spin_lock_irqsave(&ucounts_lock, flags);
    + if (ucounts->count == INT_MAX)
    + WARN_ONCE(1, "ucounts: counter has reached its maximum value");
    + else
    + ucounts->count += 1;
    + spin_unlock_irqrestore(&ucounts_lock, flags);
    + }
    +
    + return ucounts;
    +}
    +
    +void set_cred_ucounts(struct cred *cred, struct user_namespace *ns, kuid_t uid)
    +{
    + struct ucounts *old = cred->ucounts;
    + if (old && old->ns == ns && uid_eq(old->uid, uid))
    + return;
    + cred->ucounts = __get_ucounts(ns, uid);
    + if (old)
    + put_ucounts(old);
    +}
    +
    +static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
    +{
    + long c, old;
    + c = atomic_long_read(v);
    for (;;) {
    if (unlikely(c >= u))
    return false;
    - old = atomic_cmpxchg(v, c, c+1);
    + old = atomic_long_cmpxchg(v, c, c+1);
    if (likely(old == c))
    return true;
    c = old;
    @@ -194,19 +220,19 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
    {
    struct ucounts *ucounts, *iter, *bad;
    struct user_namespace *tns;
    - ucounts = get_ucounts(ns, uid);
    + ucounts = __get_ucounts(ns, uid);
    for (iter = ucounts; iter; iter = tns->ucounts) {
    int max;
    tns = iter->ns;
    max = READ_ONCE(tns->ucount_max[type]);
    - if (!atomic_inc_below(&iter->ucount[type], max))
    + if (!atomic_long_inc_below(&iter->ucount[type], max))
    goto fail;
    }
    return ucounts;
    fail:
    bad = iter;
    for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
    - atomic_dec(&iter->ucount[type]);
    + atomic_long_dec(&iter->ucount[type]);

    put_ucounts(ucounts);
    return NULL;
    @@ -216,7 +242,7 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
    {
    struct ucounts *iter;
    for (iter = ucounts; iter; iter = iter->ns->ucounts) {
    - int dec = atomic_dec_if_positive(&iter->ucount[type]);
    + int dec = atomic_long_dec_if_positive(&iter->ucount[type]);
    WARN_ON_ONCE(dec < 0);
    }
    put_ucounts(ucounts);
    diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
    index af612945a4d0..4b8a4468d391 100644
    --- a/kernel/user_namespace.c
    +++ b/kernel/user_namespace.c
    @@ -1280,6 +1280,7 @@ static int userns_install(struct nsset *nsset, struct ns_common *ns)

    put_user_ns(cred->user_ns);
    set_cred_user_ns(cred, get_user_ns(user_ns));
    + set_cred_ucounts(cred, user_ns, cred->euid);

    return 0;
    }
    --
    2.29.2
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