fanotify: allow userspace to override max queue depth

fanotify has a defualt max queue depth.  This patch allows processes which
explicitly request it to have an 'unlimited' queue depth.  These processes
need to be very careful to make sure they cannot fall far enough behind
that they OOM the box.  Thus this flag is gated on CAP_SYS_ADMIN.

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

2 files changed, 11 insertions, 3 deletions

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 04f2fe47b66a..43d66d9b2eff 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -691,7 +691,14 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
                 goto out_put_group;
         }
 
-        group->max_events = FANOTIFY_DEFAULT_MAX_EVENTS;
+        if (flags & FAN_UNLIMITED_QUEUE) {
+                fd = -EPERM;
+                if (!capable(CAP_SYS_ADMIN))
+                        goto out_put_group;
+                group->max_events = UINT_MAX;
+        } else {
+                group->max_events = FANOTIFY_DEFAULT_MAX_EVENTS;
+        }
 
         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 ed479b6fef7b..e37f559c95e1 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -28,12 +28,13 @@
 #define FAN_CLASS_NOTIF         0x00000000
 #define FAN_CLASS_CONTENT       0x00000004
 #define FAN_CLASS_PRE_CONTENT   0x00000008
-
 #define FAN_ALL_CLASS_BITS      (FAN_CLASS_NOTIF | FAN_CLASS_CONTENT | \
                                  FAN_CLASS_PRE_CONTENT)
 
+#define FAN_UNLIMITED_QUEUE     0x00000010
+
 #define FAN_ALL_INIT_FLAGS      (FAN_CLOEXEC | FAN_NONBLOCK | \
-                                 FAN_ALL_CLASS_BITS)
+                                 FAN_ALL_CLASS_BITS | FAN_UNLIMITED_QUEUE)
 
 /* flags used for fanotify_modify_mark() */
 #define FAN_MARK_ADD            0x00000001