On Fri, Aug 14, 2020 at 12:14 AM linmiaohe <[email protected]> wrote: > > Willem de Bruijn <[email protected]> wrote: > >On Thu, Aug 6, 2020 at 1:48 PM linmiaohe <[email protected]> wrote: > >> > >> From: Miaohe Lin <[email protected]> > >> > >> We could be trapped in deadloop when we try to copy userspace skb > >> frags buffers to kernel with a cloned skb: > >> Reproduce code snippet: > >> skb = alloc_skb(UBUF_DATA_LEN, GFP_ATOMIC); > >> clone = skb_clone(skb, GFP_ATOMIC); > >> skb_zcopy_set_nouarg(clone, NULL); > >> pskb_expand_head(skb, 0, 0, GFP_ATOMIC); > >> > >> Catch this unexpected case and return -EINVAL in skb_orphan_frags() > >> before we call skb_copy_ubufs() to fix it. > > > >Is this a hypothetical codepath? > > > >skb zerocopy carefully tracks clone calls where necessary. See the call to > >skb_orphan_frags in skb_clone, and the implementation of that callee. > > > >The only caller of skb zerocopy with nouarg is tpacket_fill_skb, as of > >commit 5cd8d46ea156 ("packet: copy user buffers before orphan or clone"). > > > >As the commit subject indicates, this sets skb_zcopy_set_nouarg exactly to > >be sure that any clone will trigger a copy of "zerocopy" > >user data to private kernel memory. > > > >No clone must happen between alloc_skb and skb_zcopy_set_nouarg, indeed. But > >AFAIK, none exists. > > Since we always call skb_orphan_frags in skb_clone, is it unnecessary to call > skb_orphan_frags in pskb_expand_head when skb is cloned ?
Please give us a real case. I fear that your patches are coming directly from some kind of automated tool, that really misses how the code is really used from _current_ code base, not _hypothetical_ one. This is very time consuming. Please provide evidence first. Thank you.
