inotify: Convert to using per-namespace limits

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. Additionally, in order to preserve the
sysctl ABI make the existing inotify instances/watches sysctls
modify the values of the initial user namespace.

Signed-off-by: Nikolay Borisov <n.borisov.lkml@gmail.com>
Acked-by: Jan Kara <jack@suse.cz>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

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 inline void dec_inotify_instances(struct ucounts *ucounts)
+{
+	dec_ucount(ucounts, UCOUNT_INOTIFY_INSTANCES);
+}
+
+static inline struct ucounts *inc_inotify_watches(struct ucounts *ucounts)
+{
+	return inc_ucount(ucounts->ns, ucounts->uid, UCOUNT_INOTIFY_WATCHES);
+}
+
+static inline void dec_inotify_watches(struct ucounts *ucounts)
+{
+	dec_ucount(ucounts, UCOUNT_INOTIFY_WATCHES);
+}
+#endif

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)

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;
 
@@ -60,7 +58,7 @@ static int zero;
 struct ctl_table inotify_table[] = {
 	{
 		.procname	= "max_user_instances",
-		.data		= &inotify_max_user_instances,
+		.data		= &init_user_ns.ucount_max[UCOUNT_INOTIFY_INSTANCES],
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
@@ -68,7 +66,7 @@ struct ctl_table inotify_table[] = {
 	},
 	{
 		.procname	= "max_user_watches",
-		.data		= &inotify_max_user_watches,
+		.data		= &init_user_ns.ucount_max[UCOUNT_INOTIFY_WATCHES],
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
@@ -500,7 +498,7 @@ 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 +582,17 @@ 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 +602,6 @@ 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 +652,11 @@ 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 +819,8 @@ 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;
 }

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
@@ -170,7 +171,7 @@ 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

include/linux/sched.h

@@ -868,10 +868,6 @@ 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

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,
 };
 

kernel/ucount.c

@@ -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 */