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[2a00:1028:838d:271e:8e3b:4aff:fe4c:a100]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48de0ab4f34sm10988702f8f.28.2026.10.14.02.23.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Oct 2026 02:23:34 -0700 (PDT) Message-ID: Date: Wed, 14 Oct 2026 11:23:33 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH module v2] module: Fix uninitialized count read of unloaded taint tracking record To: Binbin Deng <18983559317@163.com> Cc: mcgrof@kernel.org, da.gomez@kernel.org, samitolvanen@google.com, atomlin@atomlin.com, linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261010080356.6596-1-18983559317@163.com> Content-Language: en-US From: Petr Pavlu In-Reply-To: <20261010080356.6596-1-18983559317@163.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/10/26 10:03 AM, Binbin Deng wrote: > try_add_tainted_module() allocates the tracking record without zeroing > it and initializes the fields in this order: > > mod_taint = kmalloc_obj(*mod_taint); > strscpy(mod_taint->name, mod->name, MODULE_NAME_LEN); > mod_taint->taints = mod->taints; > list_add_rcu(&mod_taint->list, &unloaded_tainted_modules); > mod_taint->count = 1; > > The record is published by list_add_rcu() before the count field is > written. The readers, unloaded_tainted_modules_seq_show() (debugfs, > under rcu_read_lock()) and print_unloaded_tainted_modules() (panic > path, under guard(rcu)), traverse the list under RCU and read > mod_taint->count. module_mutex, which the writer holds, does not > exclude RCU readers. > > A reader that observes the new node between the list_add_rcu() and > the count store reads an uninitialized u64 left over from previous > slab use. This is a data race and leaks kernel heap residue through > the debugfs file and the panic message. > > The race window is two adjacent instructions; it is reachable when a > tainted module is unloaded (rmmod) concurrently with a read of > /sys/kernel/debug/module/unloaded_tainted, or with the module list > printout of an oops on another CPU. > > Fix this by initializing count before the record is published. > > Found during a static-analysis-assisted audit: candidate sites were > surfaced by a Coccinelle rule, and the reader/writer paths were > confirmed by LLM-assisted (GLM-5.3) code inspection. The issue was > not observed at runtime; it is identified by code inspection only. > > Fixes: 99bd9956551b ("module: Introduce module unload taint tracking") > Signed-off-by: Binbin Deng <18983559317@163.com> Looks ok, I've queued the patch on modules-next for v7.4-rc1. -- Thanks, Petr