Patch "virtio-console: avoid DMA from stack" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

virtio-console: avoid DMA from stack

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
virtio-console-avoid-dma-from-stack.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Omar Sandoval <[email protected]>
Date: Wed, 1 Feb 2017 00:02:27 -0800
Subject: virtio-console: avoid DMA from stack

From: Omar Sandoval <[email protected]>

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).

---
 drivers/char/virtio_console.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

@@ -1130,6 +1130,8 @@ 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);

@@ -1138,8 +1140,14 @@ 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;
 }
 
 /*

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/virtio-console-avoid-dma-from-stack.patch