Re: [PATCH 4.16 231/272] fanotify: Avoid lost events due to ENOMEM for unlimited queues

On Mon, May 28, 2018 at 1:04 PM, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:

4.16-stable review patch. If anyone has any objections, please let me know.

I do not have objections for applying this patch to stable, but AFAIK it is a correctness patch that doesn't fix any bug and it was mainly added as a prerequisite to memcg accounting of event allocations, which is not yet merged and not destined for stable.

Jan? do you agree with my statements above?

Thanks, Amir.

---

From: Jan Kara jack@suse.cz

[ Upstream commit 1f5eaa90010ed7cf0ae90a526c48657d02c6086f ]

Fanotify queues of unlimited length do not expect events can be lost. Since these queues are used for system auditing and other security related tasks, loosing events can even have security implications. Currently, since the allocation is small (32-bytes), it cannot fail however when we start accounting events in memcgs, allocation can start failing. So avoid loosing events due to failure to allocate memory by making event allocation use __GFP_NOFAIL.

Reviewed-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

---

fs/notify/fanotify/fanotify.c | 19 ++++++++++++++----- fs/notify/fanotify/fanotify.h | 3 ++- fs/notify/fanotify/fanotify_user.c | 2 +- 3 files changed, 17 insertions(+), 7 deletions(-)

--- a/fs/notify/fanotify/fanotify.c +++ b/fs/notify/fanotify/fanotify.c @@ -135,23 +135,32 @@ static bool fanotify_should_send_event(s return false; }

-struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask, +struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,

•                                            struct inode *inode, u32 mask,
                                             const struct path *path)
  

{ struct fanotify_event_info *event;

•   gfp_t gfp = GFP_KERNEL;
  

•   /*
  

•    * For queues with unlimited length lost events are not expected and
  

•    * can possibly have security implications. Avoid losing events when
  

•    * memory is short.
  

•    */
  

•   if (group->max_events == UINT_MAX)
  

•           gfp |= __GFP_NOFAIL;
  
    if (fanotify_is_perm_event(mask)) {
            struct fanotify_perm_event_info *pevent;
  
  

•           pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
  

•                                     GFP_KERNEL);
  

•           pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
            if (!pevent)
                    return NULL;
            event = &pevent->fae;
            pevent->response = 0;
            goto init;
    }
  

•   event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
  

•   event = kmem_cache_alloc(fanotify_event_cachep, gfp);
    if (!event)
            return NULL;
  

init: __maybe_unused @@ -206,7 +215,7 @@ static int fanotify_handle_event(struct return 0; }

•   event = fanotify_alloc_event(inode, mask, data);
  

•   event = fanotify_alloc_event(group, inode, mask, data);
    ret = -ENOMEM;
    if (unlikely(!event))
            goto finish;
  

--- a/fs/notify/fanotify/fanotify.h +++ b/fs/notify/fanotify/fanotify.h @@ -52,5 +52,6 @@ static inline struct fanotify_event_info return container_of(fse, struct fanotify_event_info, fse); }

-struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask, +struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,

•                                            struct inode *inode, u32 mask,
                                             const struct path *path);
  

--- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -757,7 +757,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned group->fanotify_data.user = user; atomic_inc(&user->fanotify_listeners);

•   oevent = fanotify_alloc_event(NULL, FS_Q_OVERFLOW, NULL);
  

•   oevent = fanotify_alloc_event(group, NULL, FS_Q_OVERFLOW, NULL);
    if (unlikely(!oevent)) {
            fd = -ENOMEM;
            goto out_destroy_group;