On Sat, Dec 23, 2017 at 01:25:05AM +0100, Andrea Arcangeli wrote:
> The previous fix 384632e67e0829deb8015ee6ad916b180049d252 corrected
> the refcounting in case of UFFD_EVENT_FORK failure for the fork
> userfault paths. That still didn't clear the vma->vm_userfaultfd_ctx
> of the vmas that were set to point to the aborted new uffd ctx earlier
> in dup_userfaultfd.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> ---
> fs/userfaultfd.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 896f810b6a06..1a88916455bd 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -591,11 +591,14 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason)
> static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
> struct userfaultfd_wait_queue *ewq)
> {
> + struct userfaultfd_ctx *release_new_ctx;
Nit: we could have set release_new_ctx to NULL here...
> +
> if (WARN_ON_ONCE(current->flags & PF_EXITING))
> goto out;
>
> ewq->ctx = ctx;
> init_waitqueue_entry(&ewq->wq, current);
> + release_new_ctx = NULL;
>
> spin_lock(&ctx->event_wqh.lock);
> /*
> @@ -622,8 +625,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
> new = (struct userfaultfd_ctx *)
> (unsigned long)
> ewq->msg.arg.reserved.reserved1;
> -
> - userfaultfd_ctx_put(new);
> + release_new_ctx = new;
> }
> break;
> }
> @@ -638,6 +640,20 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
> __set_current_state(TASK_RUNNING);
> spin_unlock(&ctx->event_wqh.lock);
>
> + if (release_new_ctx) {
> + struct vm_area_struct *vma;
> + struct mm_struct *mm = release_new_ctx->mm;
> +
> + /* the various vma->vm_userfaultfd_ctx still points to it */
> + down_write(&mm->mmap_sem);
> + for (vma = mm->mmap; vma; vma = vma->vm_next)
> + if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx)
> + vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> + up_write(&mm->mmap_sem);
> +
> + userfaultfd_ctx_put(release_new_ctx);
> + }
> +
> /*
> * ctx may go away after this if the userfault pseudo fd is
> * already released.
>
--
Sincerely yours,
Mike.
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