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[92.59.2.29]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a1bd640be0sm30545e9.1.2026.10.14.07.51.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Oct 2026 07:51:05 -0700 (PDT) Sender: Julian Braha Message-ID: <95cb289c-384d-495e-91d4-bd7dd4d2a12a@gmail.com> Date: Wed, 14 Oct 2026 15:51:03 +0100 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 v2] kconfig: fix use-after-free when a variable refers to itself To: Leizhen Zhang , nathan@kernel.org, nsc@kernel.org Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261008164504.3683811-1-lzsx618@gmail.com> Content-Language: en-US From: Julian Braha In-Reply-To: <20261008164504.3683811-1-lzsx618@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/8/26 17:45, Leizhen Zhang wrote: > For a simply expanded variable, variable_add() frees the old value of an > existing variable (or allocates a new variable with an uninitialized > value) before expanding the right-hand side. If the right-hand side > refers to the variable itself, which is a common idiom in Makefiles, > e.g. > > X := 1 > X := $(X) 2 > > the expansion reads the freed (or uninitialized) value. With ASan this > is reported as a heap-use-after-free, or a SEGV if X was undefined. > Without ASan, X silently ends up as " 2" instead of "1 2". > > Expand the right-hand side before updating the variable, initialize the > value of a newly created variable, and only free the old value when it > is actually replaced. Add a test case for this. > > Found by fuzzing Kconfig input with ASan/UBSan. > > Fixes: 1175c02506ff ("kconfig: support simply expanded variable") > Assisted-by: Claude:claude-opus-5-5 ASan UBSan libFuzzer > Signed-off-by: Leizhen Zhang Tested-by: Julian Braha Reviewed-by: Julian Braha