fanotify: permissions and blocking

This is the backend work needed for fanotify to support the new
FS_OPEN_PERM and FS_ACCESS_PERM fsnotify events.  This is done using the
new fsnotify secondary queue.  No userspace interface is provided actually
respond to or request these events.

Signed-off-by: Eric Paris <eparis@redhat.com>

5 files changed, 99 insertions, 4 deletions

diff --git a/fs/notify/fanotify/Kconfig b/fs/notify/fanotify/Kconfig
index 668e5df28e2..566de30395c 100644
--- a/fs/notify/fanotify/Kconfig
+++ b/fs/notify/fanotify/Kconfig
@@ -10,3 +10,17 @@ config FANOTIFY
            the event.
 
            If unsure, say Y.
+
+config FANOTIFY_ACCESS_PERMISSIONS
+        bool "fanotify permissions checking"
+        depends on FANOTIFY
+        depends on SECURITY
+        default n
+        ---help---
+           Say Y here is you want fanotify listeners to be able to make permissions
+           decisions concerning filesystem events.  This is used by some fanotify
+           listeners which need to scan files before allowing the system access to
+           use those files.  This is used by some anti-malware vendors and by some
+           hierarchical storage managent systems.
+
+           If unsure, say N.
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 4feed8601e2..52d0a55a249 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -2,9 +2,12 @@
 #include <linux/fdtable.h>
 #include <linux/fsnotify_backend.h>
 #include <linux/init.h>
+#include <linux/jiffies.h>
 #include <linux/kernel.h> /* UINT_MAX */
 #include <linux/mount.h>
+#include <linux/sched.h>
 #include <linux/types.h>
+#include <linux/wait.h>
 
 static bool should_merge(struct fsnotify_event *old, struct fsnotify_event *new)
 {
@@ -88,10 +91,37 @@ out:
         return ret;
 }
 
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+static int fanotify_get_response_from_access(struct fsnotify_group *group,
+                                             struct fsnotify_event *event)
+{
+        int ret;
+
+        pr_debug("%s: group=%p event=%p\n", __func__, group, event);
+
+        wait_event(group->fanotify_data.access_waitq, event->response);
+
+        /* userspace responded, convert to something usable */
+        spin_lock(&event->lock);
+        switch (event->response) {
+        case FAN_ALLOW:
+                ret = 0;
+                break;
+        case FAN_DENY:
+        default:
+                ret = -EPERM;
+        }
+        event->response = 0;
+        spin_unlock(&event->lock);
+
+        return ret;
+}
+#endif
+
 static int fanotify_handle_event(struct fsnotify_group *group, struct fsnotify_event *event)
 {
         int ret;
-        struct fsnotify_event *used_event;
+        struct fsnotify_event *notify_event = NULL;
 
         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
@@ -100,15 +130,31 @@ static int fanotify_handle_event(struct fsnotify_group *group, struct fsnotify_e
         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
+        BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
+        BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 
         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-        ret = fsnotify_add_notify_event(group, event, NULL, fanotify_merge, (void **)&used_event);
+        ret = fsnotify_add_notify_event(group, event, NULL, fanotify_merge,
+                                        (void **)&notify_event);
         /* -EEXIST means this event was merged with another, not that it was an error */
         if (ret == -EEXIST)
                 ret = 0;
-        if (used_event)
-                fsnotify_put_event(used_event);
+        if (ret)
+                goto out;
+
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+        if (event->mask & FAN_ALL_PERM_EVENTS) {
+                /* if we merged we need to wait on the new event */
+                if (notify_event)
+                        event = notify_event;
+                ret = fanotify_get_response_from_access(group, event);
+        }
+#endif
+
+out:
+        if (notify_event)
+                fsnotify_put_event(notify_event);
         return ret;
 }
 
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 84d3e2047de..09d9bdb62af 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -482,6 +482,11 @@ SYSCALL_DEFINE3(fanotify_init, unsigned int, flags, unsigned int, event_f_flags,
                 return PTR_ERR(group);
 
         group->priority = priority;
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+        mutex_init(&group->fanotify_data.access_mutex);
+        init_waitqueue_head(&group->fanotify_data.access_waitq);
+        INIT_LIST_HEAD(&group->fanotify_data.access_list);
+#endif
 
         fd = anon_inode_getfd("[fanotify]", &fanotify_fops, group, f_flags);
         if (fd < 0)
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 385896c9f82..02f80676c23 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -15,6 +15,9 @@
 /* FIXME currently Q's have no limit.... */
 #define FAN_Q_OVERFLOW          0x00004000      /* Event queued overflowed */
 
+#define FAN_OPEN_PERM           0x00010000      /* File open in perm check */
+#define FAN_ACCESS_PERM         0x00020000      /* File accessed in perm check */
+
 /* helper events */
 #define FAN_CLOSE               (FAN_CLOSE_WRITE | FAN_CLOSE_NOWRITE) /* close */
 
@@ -52,7 +55,14 @@
                         FAN_CLOSE |\
                         FAN_OPEN)
 
+/*
+ * All events which require a permission response from userspace
+ */
+#define FAN_ALL_PERM_EVENTS (FAN_OPEN_PERM |\
+                             FAN_ACCESS_PERM)
+
 #define FAN_ALL_OUTGOING_EVENTS (FAN_ALL_EVENTS |\
+                                 FAN_ALL_PERM_EVENTS |\
                                  FAN_Q_OVERFLOW)
 
 #define FANOTIFY_METADATA_VERSION       1
@@ -65,6 +75,10 @@ struct fanotify_event_metadata {
         __s64 pid;
 } __attribute__ ((packed));
 
+/* Legit userspace responses to a _PERM event */
+#define FAN_ALLOW       0x01
+#define FAN_DENY        0x02
+
 /* Helper functions to deal with fanotify_event_metadata buffers */
 #define FAN_EVENT_METADATA_LEN (sizeof(struct fanotify_event_metadata))
 
@@ -78,5 +92,9 @@ struct fanotify_event_metadata {
 
 #ifdef __KERNEL__
 
+struct fanotify_wait {
+        struct fsnotify_event *event;
+        __s32 fd;
+};
 #endif /* __KERNEL__ */
 #endif /* _LINUX_FANOTIFY_H */
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index c34728e7d8c..b0d00fd6bfa 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -160,6 +160,14 @@ struct fsnotify_group {
                         struct user_struct      *user;
                 } inotify_data;
 #endif
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+                struct fanotify_group_private_data {
+                        /* allows a group to block waiting for a userspace response */
+                        struct mutex access_mutex;
+                        struct list_head access_list;
+                        wait_queue_head_t access_waitq;
+                } fanotify_data;
+#endif
         };
 };
 
@@ -227,6 +235,10 @@ struct fsnotify_event {
         size_t name_len;
         struct pid *tgid;
 
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+        __u32 response; /* userspace answer to question */
+#endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */
+
         struct list_head private_data_list;     /* groups can store private data here */
 };