lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAKhg4t+omfRPP3pe4Suq65GiJCT2QtpB=6f+T=dWrmu7_SrZZQ@mail.gmail.com> Date: Thu, 6 Apr 2023 11:28:03 +0800 From: Liang Chen <liangchen.linux@...il.com> To: Alexander Duyck <alexander.duyck@...il.com> Cc: Jakub Kicinski <kuba@...nel.org>, ilias.apalodimas@...aro.org, hawk@...nel.org, davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com, netdev@...r.kernel.org Subject: Re: [PATCH] skbuff: Fix a race between coalescing and releasing SKBs On Wed, Apr 5, 2023 at 11:06 PM Alexander Duyck <alexander.duyck@...il.com> wrote: > > On Wed, Apr 5, 2023 at 1:19 AM Liang Chen <liangchen.linux@...il.com> wrote: > > > > On Wed, Apr 5, 2023 at 9:21 AM Jakub Kicinski <kuba@...nel.org> wrote: > > > > > > On Tue, 04 Apr 2023 08:51:18 -0700 Alexander H Duyck wrote: > > > > I'm not quite sure I agree with the fix. Couldn't we just modify the > > > > check further down that does: > > > > > > > > if (!skb_cloned(from)) > > > > from_shinfo->nr_frags = 0; > > > > > > > > And instead just make that: > > > > if (!skb->cloned || (!skb_cloned(from) && !from->pp_recycle)) > > > > from_shinfo->nr_frags = 0; > > > > > > > > With that we would retain the existing behavior and in the case of > > > > cloned from frames we would take the references and let the original > > > > from skb freed to take care of pulling the pages from the page pool. > > > > > > Sounds like a better fix, indeed. But this sort of code will require > > > another fat comment above to explain why. This: > > > > > > if (to->pp_recycle == from->pp_recycle && !skb_cloned(from)) > > > > > > is much easier to understand, no? > > > > > > We should at least include that in the explanatory comment, I reckon... > > > > Sure, the idea of dealing with the case where @from transitioned into non cloned > > skb in the function retains the existing behavior, and gives more > > opportunities to > > coalesce skbs. And it seems (!skb_cloned(from) && !from->pp_recycle) is enough > > here. > > I will take a closer look at the code path for the fragstolen case > > before making v2 > > patch - If @from transitioned into non cloned skb before "if > > (skb_head_is_locked(from))" > > > > Thanks for the reviews. > > Actually I am not sure that works now that I look at it closer. The > problem with using (!skb_cloned(from) && !from->pp_recycle) is that it > breaks the case where both from and to are pp_recycle without being > cloned. Yeah, it would break that case. Thanks! > > So it probably needs to be something actually the setup Jakub > suggested would probably work better: > if (to->pp_recycle == from->pp_recycle && !skb_cloned(from)) > I agree. That's better. > Basically we just have to guarantee that if we are copying frags over > the frag destructor is the same for the origin and destination. > Otherwise we can take a reference and convert them to being reference > counted.
Powered by blists - more mailing lists