Re: [PATCH v2 2/2] ucounts: Move rlimit max values from ucounts max

Eric W. Biederman
2021-12-13T15:50:57Z

Alexey Gladkov <legion@kernel.org> writes:

> Since the semantics of maximum rlimit values are different, they need to
> be separated from ucount_max. This will prevent the error of using
> inc_count/dec_ucount for rlimit parameters.
>
> This patch also renames the functions to emphasize the lack of
> connection between rlimit_max and ucount_max.
>
> v2:
> - Fix the array-index-out-of-bounds that was found by the lkp project.

Just looking at this I wonder if it things would come out cleaner if we
had a separate "enum ucount_rlimit_type" and a separate array in "struct
ucount" for the rlimits.

Just so that people don't accidentally mix the two.

>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Signed-off-by: Alexey Gladkov <legion@kernel.org>
> ---
> include/linux/user_namespace.h | 17 ++++++++++++-----
> kernel/fork.c | 10 +++++-----
> kernel/ucount.c | 10 +++-------
> kernel/user_namespace.c | 10 +++++-----
> 4 files changed, 25 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 33a4240e6a6f..812b6935f4a3 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -58,10 +58,11 @@ enum ucount_type {
> UCOUNT_RLIMIT_MSGQUEUE,
> UCOUNT_RLIMIT_SIGPENDING,
> UCOUNT_RLIMIT_MEMLOCK,
> - UCOUNT_COUNTS,
> + UCOUNT_ALL_COUNTS,
> };
>
> -#define MAX_PER_NAMESPACE_UCOUNTS UCOUNT_RLIMIT_NPROC
> +#define UCOUNT_COUNTS UCOUNT_RLIMIT_NPROC
> +#define RLIMIT_COUNTS UCOUNT_ALL_COUNTS - UCOUNT_COUNTS + 1
>
> struct user_namespace {
> struct uid_gid_map uid_map;
> @@ -99,6 +100,7 @@ struct user_namespace {
> #endif
> struct ucounts *ucounts;
> long ucount_max[UCOUNT_COUNTS];
> + long rlimit_max[RLIMIT_COUNTS];
> } __randomize_layout;
>
> struct ucounts {
> @@ -106,7 +108,7 @@ struct ucounts {
> struct user_namespace *ns;
> kuid_t uid;
> atomic_t count;
> - atomic_long_t ucount[UCOUNT_COUNTS];
> + atomic_long_t ucount[UCOUNT_ALL_COUNTS];
> };
>
> extern struct user_namespace init_user_ns;
> @@ -131,10 +133,15 @@ long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum ucount_type type);
> void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum ucount_type type);
> bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max);
>
> -static inline void set_rlimit_ucount_max(struct user_namespace *ns,
> +static inline long get_userns_rlimit_max(struct user_namespace *ns, enum ucount_type type)
> +{
> + return READ_ONCE(ns->rlimit_max[type - UCOUNT_COUNTS]);
> +}
> +
> +static inline void set_userns_rlimit_max(struct user_namespace *ns,
> enum ucount_type type, unsigned long max)
> {
> - ns->ucount_max[type] = max <= LONG_MAX ? max : LONG_MAX;
> + ns->rlimit_max[type - UCOUNT_COUNTS] = max <= LONG_MAX ? max : LONG_MAX;
> }
>
> #ifdef CONFIG_USER_NS
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 3244cc56b697..365819458030 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -836,13 +836,13 @@ void __init fork_init(void)
> init_task.signal->rlim[RLIMIT_SIGPENDING] =
> init_task.signal->rlim[RLIMIT_NPROC];
>
> - for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++)
> + for (i = 0; i < UCOUNT_COUNTS; i++)
> init_user_ns.ucount_max[i] = max_threads/2;
>
> - set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_NPROC, RLIM_INFINITY);
> - set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MSGQUEUE, RLIM_INFINITY);
> - set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_SIGPENDING, RLIM_INFINITY);
> - set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MEMLOCK, RLIM_INFINITY);
> + set_userns_rlimit_max(&init_user_ns, UCOUNT_RLIMIT_NPROC, RLIM_INFINITY);
> + set_userns_rlimit_max(&init_user_ns, UCOUNT_RLIMIT_MSGQUEUE, RLIM_INFINITY);
> + set_userns_rlimit_max(&init_user_ns, UCOUNT_RLIMIT_SIGPENDING, RLIM_INFINITY);
> + set_userns_rlimit_max(&init_user_ns, UCOUNT_RLIMIT_MEMLOCK, RLIM_INFINITY);
>
> #ifdef CONFIG_VMAP_STACK
> cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 7b32c356ebc5..ffffcfae8474 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -87,10 +87,6 @@ static struct ctl_table user_table[] = {
> UCOUNT_ENTRY("max_fanotify_groups"),
> UCOUNT_ENTRY("max_fanotify_marks"),
> #endif
> - { },
> - { },
> - { },
> - { },
> { }
> };
> #endif /* CONFIG_SYSCTL */
> @@ -273,7 +269,7 @@ long inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
> ret = LONG_MAX;
> else if (iter == ucounts)
> ret = new;
> - max = READ_ONCE(iter->ns->ucount_max[type]);
> + max = get_userns_rlimit_max(iter->ns, type);
> }
> return ret;
> }
> @@ -322,7 +318,7 @@ long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum ucount_type type)
> goto unwind;
> if (iter == ucounts)
> ret = new;
> - max = READ_ONCE(iter->ns->ucount_max[type]);
> + max = get_userns_rlimit_max(iter->ns, type);
> /*
> * Grab an extra ucount reference for the caller when
> * the rlimit count was previously 0.
> @@ -350,7 +346,7 @@ bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsign
> for (iter = ucounts; iter; iter = iter->ns->ucounts) {
> if (get_ucounts_value(iter, type) > max)
> return true;
> - max = READ_ONCE(iter->ns->ucount_max[type]);
> + max = get_userns_rlimit_max(iter->ns, type);
> }
> return false;
> }
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 6b2e3ca7ee99..b9f6729b4e5f 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -119,13 +119,13 @@ int create_user_ns(struct cred *new)
> ns->owner = owner;
> ns->group = group;
> INIT_WORK(&ns->work, free_user_ns);
> - for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++) {
> + for (i = 0; i < UCOUNT_COUNTS; i++) {
> ns->ucount_max[i] = INT_MAX;
> }
> - set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC));
> - set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_MSGQUEUE, rlimit(RLIMIT_MSGQUEUE));
> - set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_SIGPENDING, rlimit(RLIMIT_SIGPENDING));
> - set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_MEMLOCK, rlimit(RLIMIT_MEMLOCK));
> + set_userns_rlimit_max(ns, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC));
> + set_userns_rlimit_max(ns, UCOUNT_RLIMIT_MSGQUEUE, rlimit(RLIMIT_MSGQUEUE));
> + set_userns_rlimit_max(ns, UCOUNT_RLIMIT_SIGPENDING, rlimit(RLIMIT_SIGPENDING));
> + set_userns_rlimit_max(ns, UCOUNT_RLIMIT_MEMLOCK, rlimit(RLIMIT_MEMLOCK));
> ns->ucounts = ucounts;
>
> /* Inherit USERNS_SETGROUPS_ALLOWED from our parent */