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([2a02:aa16:1105:8100:157a:cab0:dc27:cd03]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4909c0c39b0sm25645315e9.2.2026.05.29.06.59.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 29 May 2026 06:59:45 -0700 (PDT) Message-ID: Date: Fri, 29 May 2026 15:59:44 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] netdevsim: fib: fix use-after-free of FIB data via debugfs To: Ido Schimmel Cc: Jakub Kicinski , Andrew Lunn , "David S . Miller" , Eric Dumazet , Paolo Abeni , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260526160910.1614609-1-yzjaurora@gmail.com> <20260527083214.GA444725@shredder> Content-Language: en-US From: Zijing yin In-Reply-To: <20260527083214.GA444725@shredder> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Thanks so much for the feedback! I have sent the revised patch accordingly: https://lore.kernel.org/netdev/20260529135718.1804031-1-yzjaurora@gmail.com/T/#u Hope you have a nice weekend! On 27.05.2026 10:32, Ido Schimmel wrote: > On Tue, May 26, 2026 at 09:09:08AM -0700, Zijing Yin wrote: >> @@ -1600,6 +1597,16 @@ struct nsim_fib_data *nsim_fib_create(struct devlink *devlink, >> goto err_nexthop_nb_unregister; >> } >> >> + /* Publish the debugfs interface only after every data structure it >> + * operates on has been initialized. The files reference this >> + * nsim_fib_data (e.g. "nexthop_bucket_activity" looks up >> + * data->nexthop_ht), so a concurrent debugfs access must never be able >> + * to observe a half-constructed instance. >> + */ >> + err = nsim_fib_debugfs_init(data, nsim_dev); >> + if (err) >> + goto err_fib_notifier_unregister; >> + >> devl_resource_occ_get_register(devlink, >> NSIM_RESOURCE_IPV4_FIB, >> nsim_fib_ipv4_resource_occ_get, >> @@ -1622,6 +1629,8 @@ struct nsim_fib_data *nsim_fib_create(struct devlink *devlink, >> data); >> return data; >> >> +err_fib_notifier_unregister: >> + unregister_fib_notifier(devlink_net(devlink), &data->fib_nb); >> err_nexthop_nb_unregister: >> unregister_nexthop_notifier(devlink_net(devlink), &data->nexthop_nb); >> err_rhashtable_fib_destroy: >> @@ -1633,16 +1642,23 @@ struct nsim_fib_data *nsim_fib_create(struct devlink *devlink, >> rhashtable_free_and_destroy(&data->nexthop_ht, nsim_nexthop_free, >> data); >> mutex_destroy(&data->fib_lock); >> -err_debugfs_exit: >> +err_nh_lock_destroy: >> mutex_destroy(&data->nh_lock); >> - nsim_fib_debugfs_exit(data); >> -err_data_free: >> kfree(data); >> return ERR_PTR(err); >> } >> >> void nsim_fib_destroy(struct devlink *devlink, struct nsim_fib_data *data) >> { >> + /* Tear down the debugfs files before freeing the data structures they >> + * operate on. debugfs_remove_recursive() waits for any in-flight file >> + * operation (e.g. a write to "fib/nexthop_bucket_activity", which looks >> + * up data->nexthop_ht) to finish and prevents new ones from starting, >> + * so the rhashtables are not freed while a concurrent accessor still >> + * dereferences them. >> + */ >> + nsim_fib_debugfs_exit(data); > > Thanks for the patch. Let's try to keep both functions symmetric: > > Call nsim_fib_debugfs_exit() just before unregister_fib_notifier(). > > Also, I would drop the comments. > >> + >> devl_resource_occ_get_unregister(devlink, >> NSIM_RESOURCE_NEXTHOPS); >> devl_resource_occ_get_unregister(devlink, >> @@ -1665,6 +1681,5 @@ void nsim_fib_destroy(struct devlink *devlink, struct nsim_fib_data *data) >> WARN_ON_ONCE(!list_empty(&data->fib_rt_list)); >> mutex_destroy(&data->fib_lock); >> mutex_destroy(&data->nh_lock); >> - nsim_fib_debugfs_exit(data); >> kfree(data); >> } >> -- >> 2.43.0 >>