linux-kernel - [PATCH 3.16 197/212] virtio-console: avoid DMA from stack

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Message-ID: <lsq.1496331796.351957956@decadent.org.uk>
Date:   Thu, 01 Jun 2017 16:43:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Michael S. Tsirkin" <mst@...hat.com>,
        "Amit Shah" <amit.shah@...hat.com>,
        "Omar Sandoval" <osandov@...com>
Subject: [PATCH 3.16 197/212] virtio-console: avoid DMA from stack

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Omar Sandoval <osandov@...com>

commit c4baad50297d84bde1a7ad45e50c73adae4a2192 upstream.

put_chars() stuffs the buffer it gets into an sg, but that buffer may be
on the stack. This breaks with CONFIG_VMAP_STACK=y (for me, it
manifested as printks getting turned into NUL bytes).

Signed-off-by: Omar Sandoval <osandov@...com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Reviewed-by: Amit Shah <amit.shah@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/char/virtio_console.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1129,6 +1129,8 @@ static int put_chars(u32 vtermno, const
 {
 	struct port *port;
 	struct scatterlist sg[1];
+	void *data;
+	int ret;
 
 	if (unlikely(early_put_chars))
 		return early_put_chars(vtermno, buf, count);
@@ -1137,8 +1139,14 @@ static int put_chars(u32 vtermno, const
 	if (!port)
 		return -EPIPE;
 
-	sg_init_one(sg, buf, count);
-	return __send_to_port(port, sg, 1, count, (void *)buf, false);
+	data = kmemdup(buf, count, GFP_ATOMIC);
+	if (!data)
+		return -ENOMEM;
+
+	sg_init_one(sg, data, count);
+	ret = __send_to_port(port, sg, 1, count, data, false);
+	kfree(data);
+	return ret;
 }
 
 /*