From:   Pavel Skripkin <paskripkin@gmail.com>
To:     kraxel@redhat.com, sumit.semwal@linaro.org,
        christian.koenig@amd.com, daniel.vetter@ffwll.ch
Cc:     dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org,
        linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org,
        Pavel Skripkin <paskripkin@gmail.com>,
        syzbot+2c56b725ec547fa9cb29@syzkaller.appspotmail.com
Subject: [PATCH] udmabuf: validate ubuf->pagecount
Date:   Thu, 30 Dec 2021 17:26:49 +0300
Message-Id: <20211230142649.23022-1-paskripkin@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Syzbot has reported GPF in sg_alloc_append_table_from_pages(). The
problem was in ubuf->pages == ZERO_PTR.

ubuf->pagecount is calculated from arguments passed from user-space. If
user creates udmabuf with list.size == 0 then ubuf->pagecount will be
also equal to zero; it causes kmalloc_array() to return ZERO_PTR.

Fix it by validating ubuf->pagecount before passing it to
kmalloc_array().

Fixes: fbb0de795078 ("Add udmabuf misc device")
Reported-and-tested-by: syzbot+2c56b725ec547fa9cb29@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---

Happy New Year and Merry Christmas! :)


With regards,
Pavel Skripkin

---
 drivers/dma-buf/udmabuf.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index c57a609db75b..e7330684d3b8 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -190,6 +190,10 @@ static long udmabuf_create(struct miscdevice *device,
 		if (ubuf->pagecount > pglimit)
 			goto err;
 	}
+
+	if (!ubuf->pagecount)
+		goto err;
+
 	ubuf->pages = kmalloc_array(ubuf->pagecount, sizeof(*ubuf->pages),
 				    GFP_KERNEL);
 	if (!ubuf->pages) {
-- 
2.34.1