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Wed, 08 Apr 2026 01:28:22 -0700 (PDT) Date: Wed, 8 Apr 2026 10:28:21 +0200 From: Davide Caratti To: Jamal Hadi Salim Cc: Jiri Pirko , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Xiang Mei , netdev@vger.kernel.org, Victor Nogueira Subject: Re: [PATCH net v2] net/sched: cls_fw: fix NULL dereference of "old" filters before change() Message-ID: References: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Apr 03, 2026 at 02:59:22PM -0400, Jamal Hadi Salim wrote: > On Fri, Apr 3, 2026 at 12:04 PM Davide Caratti wrote: > > > > Like pointed out by Sashiko [1], > > Just found out about this ;-> So bye-bye old AI? ;-> > I must say, finding this specific bug is impressive. [...] > Observation on consistency pov: > You will always get a "q" when you invoke tcf_block_q() if there are > no shared blocks attached. But that doesnt mean the "create" > configuration is complete; it is only complete if step 3 above > completes. This is because we are not sure if change() will result in > "old" or "new" lookup setup. So the check you added for q may be > inconsistent from that perspective and fw should have returned -1 like > all classifiers... "Hello Jamal, you are absolutely right! (emoji with fire) However, ..." :) > I cant think of a simple solution to verify if the config is > "inconsistent" other than to add something that gets checked in the > datapath (and when absent, return -1) ^^ This. Specifically for cls_fw, that would mean converting fw_change() to allocate some control data also for the "old" uapi, and I think it's too much effort for the legacy. IIUC the inconsistent behavior is: for a small amount of time, fwmark classifier used in the "old" way would classify also when the filter's 'handle' is not zero. > From that perspective, your check is not catastrophic, so it may be ok. > At minimal the Fixes: needs to change to Vlads commit? Good news is > only fw _seems_ to suffer from this challenge... This is also what I understood by reading the code. Sure, I will edit the Fixes: tag. Thanks for reading! -- davide