Re: [PATCH net-next 1/2] tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive

[Eric Dumazet]

On 04/24/2018 10:27 PM, Eric Dumazet wrote:
> When adding tcp mmap() implementation, I forgot that socket lock
> had to be taken before current->mm->mmap_sem. syzbot eventually caught
> the bug.
> +

...

  

> +     down_read(&current->mm->mmap_sem);
> +
> +     ret = -EINVAL;
> +     vma = find_vma(current->mm, address);
> +     if (!vma || vma->vm_start > address || vma->vm_ops != &tcp_vm_ops)
>               goto out;
> -     }
> +     zc->length = min_t(unsigned long, zc->length, vma->vm_end - address);
> +
>       tp = tcp_sk(sk);
>       seq = tp->copied_seq;
> -     /* Abort if urgent data is in the area */
> -     if (unlikely(tp->urg_data)) {
> -             u32 urg_offset = tp->urg_seq - seq;
> +     zc->length = min_t(u32, zc->length, tcp_inq(sk));
>  
>

I might have to make sure zc->length is page aligned before calling 
zap_page_range() ?

zc->length &= ~(PAGE_SIZE - 1);

 +      zap_page_range(vma, address, zc->length);