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Message-ID: <8737k86n7q.fsf@x220.int.ebiederm.org>
Date: Fri, 07 Oct 2016 13:14:17 -0500
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Nikolay Borisov <kernel@...p.com>
Cc: john@...nmccutchan.com, eparis@...isplace.org,
viro@...iv.linux.org.uk, jack@...e.cz, serge@...lyn.com,
avagin@...nvz.org, linux-kernel@...r.kernel.org,
containers@...ts.linux-foundation.org
Subject: Re: [PATCH] inotify: Convert to using per-namespace limits
Nikolay Borisov <kernel@...p.com> writes:
> This patchset converts inotify to using the newly introduced
> per-userns sysctl infrastructure.
>
> Currently the inotify instances/watches are being accounted in the
> user_struct structure. This means that in setups where multiple
> users in unprivileged containers map to the same underlying
> real user (i.e. pointing to the same user_struct) the inotify limits
> are going to be shared as well, allowing one user(or application) to exhaust
> all others limits.
>
> Fix this by switching the inotify sysctls to using the
> per-namespace/per-user limits. This will allow the server admin to
> set sensible global limits, which can further be tuned inside every
> individual user namespace.
>
> Signed-off-by: Nikolay Borisov <kernel@...p.com>
> ---
> Hello Eric,
>
> I saw you've finally sent your pull request for 4.9 and it
> includes your implementatino of the ucount infrastructure. So
> here is my respin of the inotify patches using that.
Thanks. I will take a good hard look at this after -rc1 when things are
stable enough that I can start a new development branch.
I am a little concerned that the old sysctls have gone away. If no one
cares it is fine, but if someone depends on them existing that may count
as an unnecessary userspace regression. But otherwise skimming through
this code it looks good.
Eric
> fs/notify/inotify/inotify.h | 17 +++++++++++++
> fs/notify/inotify/inotify_fsnotify.c | 6 ++---
> fs/notify/inotify/inotify_user.c | 46 ++++++++++++------------------------
> include/linux/fsnotify_backend.h | 3 ++-
> include/linux/sched.h | 4 ----
> include/linux/user_namespace.h | 4 ++++
> kernel/ucount.c | 6 ++++-
> 7 files changed, 45 insertions(+), 41 deletions(-)
>
> diff --git a/fs/notify/inotify/inotify.h b/fs/notify/inotify/inotify.h
> index ed855ef6f077..b5536f8ad3e0 100644
> --- a/fs/notify/inotify/inotify.h
> +++ b/fs/notify/inotify/inotify.h
> @@ -30,3 +30,20 @@ extern int inotify_handle_event(struct fsnotify_group *group,
> const unsigned char *file_name, u32 cookie);
>
> extern const struct fsnotify_ops inotify_fsnotify_ops;
> +
> +#ifdef CONFIG_INOTIFY_USER
> +static void dec_inotify_instances(struct ucounts *ucounts)
> +{
> + dec_ucount(ucounts, UCOUNT_INOTIFY_INSTANCES);
> +}
> +
> +static struct ucounts *inc_inotify_watches(struct ucounts *ucounts)
> +{
> + return inc_ucount(ucounts->ns, ucounts->uid, UCOUNT_INOTIFY_WATCHES);
> +}
> +
> +static void dec_inotify_watches(struct ucounts *ucounts)
> +{
> + dec_ucount(ucounts, UCOUNT_INOTIFY_WATCHES);
> +}
> +#endif
> diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
> index 2cd900c2c737..1e6b3cfc2cfd 100644
> --- a/fs/notify/inotify/inotify_fsnotify.c
> +++ b/fs/notify/inotify/inotify_fsnotify.c
> @@ -165,10 +165,8 @@ static void inotify_free_group_priv(struct fsnotify_group *group)
> /* ideally the idr is empty and we won't hit the BUG in the callback */
> idr_for_each(&group->inotify_data.idr, idr_callback, group);
> idr_destroy(&group->inotify_data.idr);
> - if (group->inotify_data.user) {
> - atomic_dec(&group->inotify_data.user->inotify_devs);
> - free_uid(group->inotify_data.user);
> - }
> + if (group->inotify_data.ucounts)
> + dec_inotify_instances(group->inotify_data.ucounts);
> }
>
> static void inotify_free_event(struct fsnotify_event *fsn_event)
> diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
> index b8d08d0d0a4d..cfe48bb511c6 100644
> --- a/fs/notify/inotify/inotify_user.c
> +++ b/fs/notify/inotify/inotify_user.c
> @@ -44,10 +44,8 @@
>
> #include <asm/ioctls.h>
>
> -/* these are configurable via /proc/sys/fs/inotify/ */
> -static int inotify_max_user_instances __read_mostly;
> +/* configurable via /proc/sys/fs/inotify/ */
> static int inotify_max_queued_events __read_mostly;
> -static int inotify_max_user_watches __read_mostly;
>
> static struct kmem_cache *inotify_inode_mark_cachep __read_mostly;
>
> @@ -59,22 +57,6 @@ static int zero;
>
> struct ctl_table inotify_table[] = {
> {
> - .procname = "max_user_instances",
> - .data = &inotify_max_user_instances,
> - .maxlen = sizeof(int),
> - .mode = 0644,
> - .proc_handler = proc_dointvec_minmax,
> - .extra1 = &zero,
> - },
> - {
> - .procname = "max_user_watches",
> - .data = &inotify_max_user_watches,
> - .maxlen = sizeof(int),
> - .mode = 0644,
> - .proc_handler = proc_dointvec_minmax,
> - .extra1 = &zero,
> - },
> - {
> .procname = "max_queued_events",
> .data = &inotify_max_queued_events,
> .maxlen = sizeof(int),
> @@ -500,7 +482,7 @@ void inotify_ignored_and_remove_idr(struct fsnotify_mark *fsn_mark,
> /* remove this mark from the idr */
> inotify_remove_from_idr(group, i_mark);
>
> - atomic_dec(&group->inotify_data.user->inotify_watches);
> + dec_inotify_watches(group->inotify_data.ucounts);
> }
>
> /* ding dong the mark is dead */
> @@ -584,14 +566,17 @@ static int inotify_new_watch(struct fsnotify_group *group,
> tmp_i_mark->fsn_mark.mask = mask;
> tmp_i_mark->wd = -1;
>
> - ret = -ENOSPC;
> - if (atomic_read(&group->inotify_data.user->inotify_watches) >= inotify_max_user_watches)
> - goto out_err;
> -
> ret = inotify_add_to_idr(idr, idr_lock, tmp_i_mark);
> if (ret)
> goto out_err;
>
> + /* increment the number of watches the user has */
> + if (!inc_inotify_watches(group->inotify_data.ucounts)) {
> + inotify_remove_from_idr(group, tmp_i_mark);
> + ret = -ENOSPC;
> + goto out_err;
> + }
> +
> /* we are on the idr, now get on the inode */
> ret = fsnotify_add_mark_locked(&tmp_i_mark->fsn_mark, group, inode,
> NULL, 0);
> @@ -601,8 +586,6 @@ static int inotify_new_watch(struct fsnotify_group *group,
> goto out_err;
> }
>
> - /* increment the number of watches the user has */
> - atomic_inc(&group->inotify_data.user->inotify_watches);
>
> /* return the watch descriptor for this new mark */
> ret = tmp_i_mark->wd;
> @@ -653,10 +636,11 @@ static struct fsnotify_group *inotify_new_group(unsigned int max_events)
>
> spin_lock_init(&group->inotify_data.idr_lock);
> idr_init(&group->inotify_data.idr);
> - group->inotify_data.user = get_current_user();
> + group->inotify_data.ucounts = inc_ucount(current_user_ns(),
> + current_euid(),
> + UCOUNT_INOTIFY_INSTANCES);
>
> - if (atomic_inc_return(&group->inotify_data.user->inotify_devs) >
> - inotify_max_user_instances) {
> + if (!group->inotify_data.ucounts) {
> fsnotify_destroy_group(group);
> return ERR_PTR(-EMFILE);
> }
> @@ -819,8 +803,8 @@ static int __init inotify_user_setup(void)
> inotify_inode_mark_cachep = KMEM_CACHE(inotify_inode_mark, SLAB_PANIC);
>
> inotify_max_queued_events = 16384;
> - inotify_max_user_instances = 128;
> - inotify_max_user_watches = 8192;
> + init_user_ns.ucount_max[UCOUNT_INOTIFY_INSTANCES] = 128;
> + init_user_ns.ucount_max[UCOUNT_INOTIFY_WATCHES] = 8192;
>
> return 0;
> }
> diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> index 58205f33af02..892959de1162 100644
> --- a/include/linux/fsnotify_backend.h
> +++ b/include/linux/fsnotify_backend.h
> @@ -16,6 +16,7 @@
> #include <linux/spinlock.h>
> #include <linux/types.h>
> #include <linux/atomic.h>
> +#include <linux/user_namespace.h>
>
> /*
> * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily
> @@ -169,7 +170,7 @@ struct fsnotify_group {
> struct inotify_group_private_data {
> spinlock_t idr_lock;
> struct idr idr;
> - struct user_struct *user;
> + struct ucounts *ucounts;
> } inotify_data;
> #endif
> #ifdef CONFIG_FANOTIFY
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 62c68e513e39..35230a2c73ac 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -840,10 +840,6 @@ struct user_struct {
> atomic_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_INOTIFY_USER
> - atomic_t inotify_watches; /* How many inotify watches does this user have? */
> - atomic_t inotify_devs; /* How many inotify devs does this user have opened? */
> -#endif
> #ifdef CONFIG_FANOTIFY
> atomic_t fanotify_listeners;
> #endif
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index eb209d4523f5..cbcac7a5ec41 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -32,6 +32,10 @@ enum ucount_type {
> UCOUNT_NET_NAMESPACES,
> UCOUNT_MNT_NAMESPACES,
> UCOUNT_CGROUP_NAMESPACES,
> +#ifdef CONFIG_INOTIFY_USER
> + UCOUNT_INOTIFY_INSTANCES,
> + UCOUNT_INOTIFY_WATCHES,
> +#endif
> UCOUNT_COUNTS,
> };
>
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 9d20d5dd298a..a6bcea47306b 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -57,7 +57,7 @@ static struct ctl_table_root set_root = {
>
> static int zero = 0;
> static int int_max = INT_MAX;
> -#define UCOUNT_ENTRY(name) \
> +#define UCOUNT_ENTRY(name) \
> { \
> .procname = name, \
> .maxlen = sizeof(int), \
> @@ -74,6 +74,10 @@ static struct ctl_table user_table[] = {
> UCOUNT_ENTRY("max_net_namespaces"),
> UCOUNT_ENTRY("max_mnt_namespaces"),
> UCOUNT_ENTRY("max_cgroup_namespaces"),
> +#ifdef CONFIG_INOTIFY_USER_
> + UCOUNT_ENTRY("max_inotify_instances"),
> + UCOUNT_ENTRY("max_inotify_watches"),
> +#endif
> { }
> };
> #endif /* CONFIG_SYSCTL */
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