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>

1 files changed, 8 insertions, 1 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)