[PATCH] tee: Prevent size calculation wraparound on 32-bit kernels

[Jann Horn <jannh@google.com>]

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.

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 <jannh@google.com>
---
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 <linux/fs.h>
 #include <linux/idr.h>
 #include <linux/module.h>
+#include <linux/overflow.h>
 #include <linux/slab.h>
 #include <linux/tee_core.h>
 #include <linux/uaccess.h>
@@ -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

-- 
Jann Horn <jannh@google.com>