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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-441b276052bsm89626645e9.0.2025.05.02.05.40.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 May 2025 05:40:59 -0700 (PDT) Date: Fri, 2 May 2025 13:40:58 +0100 From: David Laight To: Jann Horn Cc: Jens Wiklander , Sumit Garg , op-tee@lists.trustedfirmware.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] tee: Prevent size calculation wraparound on 32-bit kernels Message-ID: <20250502134058.0f3e79cc@pumpkin> In-Reply-To: References: <20250428-tee-sizecheck-v1-1-5c3c25a2fa79@google.com> <20250501210158.5b2c86a7@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 2 May 2025 14:28:21 +0200 Jann Horn wrote: > On Thu, May 1, 2025 at 10:02=E2=80=AFPM David Laight > wrote: > > > > On Mon, 28 Apr 2025 15:06:43 +0200 > > Jann Horn wrote: > > =20 > > > The current code around TEE_IOCTL_PARAM_SIZE() is a bit wrong on > > > 32-bit kernels: Multiplying a user-provided 32-bit value with the > > > size of a structure can wrap around on such platforms. > > > > > > Fix it by using saturating arithmetic for the size calculation. =20 > > > > Why not just add a sanity check on 'num_params' after it is read. > > Max is 31 (1024-32)/32), but any sane limit will do because of > > the buf.buf_len test. =20 >=20 > That would work, too. I don't know which way looks nicer. The saturating arithmetic functions are non-obvious and non-trivial. I looked at the code to check where buf.buf_len came from, without its sanity check the user could craft a request where it matched the saturated size. I think I'd sanity check the number of items and then check that that buffer length is right for the number of items. David