linux-kernel - [PATCH] tee: check shm references are consistent in offset/size

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Date:   Fri, 27 Apr 2018 15:53:02 +0200
From:   Etienne Carriere <etienne.carriere@...aro.org>
To:     linux-kernel@...r.kernel.org,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alexandre Jutras <alexandre.jutras@....com>
Subject: [PATCH] tee: check shm references are consistent in offset/size

This change prevents userland from referencing TEE shared memory
outside the area initially allocated by its owner. Prior this change an
application could not reference or access memory it did not own but
it could reference memory not explicitly allocated by owner.

Reported-by: Alexandre Jutras <alexandre.jutras@....com>
Signed-off-by: Etienne Carriere <etienne.carriere@...aro.org>

---
 drivers/tee/tee_core.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
index 0124a91..dd46b75 100644
--- a/drivers/tee/tee_core.c
+++ b/drivers/tee/tee_core.c
@@ -238,6 +238,17 @@ static int params_from_user(struct tee_context
*ctx, struct tee_param *params,
             if (IS_ERR(shm))
                 return PTR_ERR(shm);

+            /*
+             * Ensure offset + size does not overflow offset
+             * and does not overflow the size of the referred
+             * shared memory object.
+             */
+            if ((ip.a + ip.b) < ip.a ||
+                (ip.a + ip.b) > shm->size) {
+                tee_shm_put(shm);
+                return -EINVAL;
+            }
+
             params[n].u.memref.shm_offs = ip.a;
             params[n].u.memref.size = ip.b;
             params[n].u.memref.shm = shm;
-- 
1.9.1