linux-kernel - Re: [PATCH net-next] net: Implement fault injection forcing skb reallocation

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Message-ID: <20241007-phenomenal-literate-hog-619ad0@leitao>
Date: Mon, 7 Oct 2024 10:09:27 -0700
From: Breno Leitao <leitao@...ian.org>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: Akinobu Mita <akinobu.mita@...il.com>, kuba@...nel.org,
	davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
	Jonathan Corbet <corbet@....net>, horms@...nel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mina Almasry <almasrymina@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH net-next] net: Implement fault injection forcing skb
 reallocation

Hello Pavel,

On Mon, Oct 07, 2024 at 05:48:39PM +0100, Pavel Begunkov wrote:
> On 10/7/24 17:20, Breno Leitao wrote:
> > On Sat, Oct 05, 2024 at 01:38:59PM +0900, Akinobu Mita wrote:
> > > 2024年10月2日(水) 20:37 Breno Leitao <leitao@...ian.org>:
> > > > 
> > > > Introduce a fault injection mechanism to force skb reallocation. The
> > > > primary goal is to catch bugs related to pointer invalidation after
> > > > potential skb reallocation.
> > > > 
> > > > The fault injection mechanism aims to identify scenarios where callers
> > > > retain pointers to various headers in the skb but fail to reload these
> > > > pointers after calling a function that may reallocate the data. This
> > > > type of bug can lead to memory corruption or crashes if the old,
> > > > now-invalid pointers are used.
> > > > 
> > > > By forcing reallocation through fault injection, we can stress-test code
> > > > paths and ensure proper pointer management after potential skb
> > > > reallocations.
> > > > 
> > > > Add a hook for fault injection in the following functions:
> > > > 
> > > >   * pskb_trim_rcsum()
> > > >   * pskb_may_pull_reason()
> > > >   * pskb_trim()
> > > > 
> > > > As the other fault injection mechanism, protect it under a debug Kconfig
> > > > called CONFIG_FAIL_SKB_FORCE_REALLOC.
> > > > 
> > > > This patch was *heavily* inspired by Jakub's proposal from:
> > > > https://lore.kernel.org/all/20240719174140.47a868e6@kernel.org/
> > > > 
> > > > CC: Akinobu Mita <akinobu.mita@...il.com>
> > > > Suggested-by: Jakub Kicinski <kuba@...nel.org>
> > > > Signed-off-by: Breno Leitao <leitao@...ian.org>
> > > 
> > > This new addition seems sensible.  It might be more useful to have a filter
> > > that allows you to specify things like protocol family.
> > 
> > I think it might make more sense to be network interface specific. For
> > instance, only fault inject in interface `ethx`.
> 
> Wasn't there some error injection infra that allows to optionally
> run bpf? That would cover the filtering problem. ALLOW_ERROR_INJECTION,
> maybe?

Isn't ALLOW_ERROR_INJECTION focused on specifying which function could
be faulted? I.e, you can mark that function as prone for fail injection?

In my the case I have in mind, I want to pass the interface that it
would have the error injected. For instance, only inject errors in
interface eth1. In this case, I am not sure ALLOW_ERROR_INJECTION will
help.

Thanks
--breno