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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a099b10083sm92350f8f.62.2025.05.01.13.01.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 May 2025 13:01:59 -0700 (PDT) Date: Thu, 1 May 2025 21:01:58 +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: <20250501210158.5b2c86a7@pumpkin> In-Reply-To: <20250428-tee-sizecheck-v1-1-5c3c25a2fa79@google.com> References: <20250428-tee-sizecheck-v1-1-5c3c25a2fa79@google.com> 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=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 28 Apr 2025 15:06:43 +0200 Jann Horn wrote: > 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. 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. David > > This has no security consequences because, in all users of > TEE_IOCTL_PARAM_SIZE(), the subsequent kcalloc() implicitly checks > for wrapping. > > Signed-off-by: Jann Horn > --- > Note that I don't have a test device with a TEE; I only compile-tested > the change on an x86-64 build. > --- > drivers/tee/tee_core.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c > index d113679b1e2d..acc7998758ad 100644 > --- a/drivers/tee/tee_core.c > +++ b/drivers/tee/tee_core.c > @@ -10,6 +10,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -19,7 +20,7 @@ > > #define TEE_NUM_DEVICES 32 > > -#define TEE_IOCTL_PARAM_SIZE(x) (sizeof(struct tee_param) * (x)) > +#define TEE_IOCTL_PARAM_SIZE(x) (size_mul(sizeof(struct tee_param), (x))) > > #define TEE_UUID_NS_NAME_SIZE 128 > > @@ -487,7 +488,7 @@ static int tee_ioctl_open_session(struct tee_context *ctx, > if (copy_from_user(&arg, uarg, sizeof(arg))) > return -EFAULT; > > - if (sizeof(arg) + TEE_IOCTL_PARAM_SIZE(arg.num_params) != buf.buf_len) > + if (size_add(sizeof(arg), TEE_IOCTL_PARAM_SIZE(arg.num_params)) != buf.buf_len) > return -EINVAL; > > if (arg.num_params) { > @@ -565,7 +566,7 @@ static int tee_ioctl_invoke(struct tee_context *ctx, > if (copy_from_user(&arg, uarg, sizeof(arg))) > return -EFAULT; > > - if (sizeof(arg) + TEE_IOCTL_PARAM_SIZE(arg.num_params) != buf.buf_len) > + if (size_add(sizeof(arg), TEE_IOCTL_PARAM_SIZE(arg.num_params)) != buf.buf_len) > return -EINVAL; > > if (arg.num_params) { > @@ -699,7 +700,7 @@ static int tee_ioctl_supp_recv(struct tee_context *ctx, > if (get_user(num_params, &uarg->num_params)) > return -EFAULT; > > - if (sizeof(*uarg) + TEE_IOCTL_PARAM_SIZE(num_params) != buf.buf_len) > + if (size_add(sizeof(*uarg), TEE_IOCTL_PARAM_SIZE(num_params)) != buf.buf_len) > return -EINVAL; > > params = kcalloc(num_params, sizeof(struct tee_param), GFP_KERNEL); > @@ -798,7 +799,7 @@ static int tee_ioctl_supp_send(struct tee_context *ctx, > get_user(num_params, &uarg->num_params)) > return -EFAULT; > > - if (sizeof(*uarg) + TEE_IOCTL_PARAM_SIZE(num_params) > buf.buf_len) > + if (size_add(sizeof(*uarg), TEE_IOCTL_PARAM_SIZE(num_params)) > buf.buf_len) > return -EINVAL; > > params = kcalloc(num_params, sizeof(struct tee_param), GFP_KERNEL); > > --- > base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e > change-id: 20250428-tee-sizecheck-299d5eff8fc7 >