linux-hardening - [PATCH] udmabuf: Fix a potential (and unlikely) access to unallocated memory

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Date:   Mon, 18 Sep 2023 20:46:35 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Gerd Hoffmann <kraxel@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org
Subject: [PATCH] udmabuf: Fix a potential (and unlikely) access to unallocated memory

If 'list_limit' is set to a very high value, 'lsize' computation could
overflow if 'head.count' is big enough.

In such a case, udmabuf_create() will access to memory beyond 'list'.

Use size_mul() to saturate the value, and have memdup_user() fail.

Fixes: fbb0de795078 ("Add udmabuf misc device")
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
 drivers/dma-buf/udmabuf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index c40645999648..fb4c4b5b3332 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -314,13 +314,13 @@ static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
 	struct udmabuf_create_list head;
 	struct udmabuf_create_item *list;
 	int ret = -EINVAL;
-	u32 lsize;
+	size_t lsize;
 
 	if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
 		return -EFAULT;
 	if (head.count > list_limit)
 		return -EINVAL;
-	lsize = sizeof(struct udmabuf_create_item) * head.count;
+	lsize = size_mul(sizeof(struct udmabuf_create_item), head.count);
 	list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
 	if (IS_ERR(list))
 		return PTR_ERR(list);
-- 
2.34.1