FAILED: patch "[PATCH] NTB: ntb_tool: uninitialized heap data in tool_fn_write()" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 45e1058b77feade4e36402828bfe3e0d3363177b Mon Sep 17 00:00:00 2001
From: Dan Carpenter <[email protected]>
Date: Wed, 20 Jul 2022 21:28:18 +0300
Subject: [PATCH] NTB: ntb_tool: uninitialized heap data in tool_fn_write()

The call to:

	ret = simple_write_to_buffer(buf, size, offp, ubuf, size);

will return success if it is able to write even one byte to "buf". The value of "*offp" controls which byte. This could result in reading uninitialized data when we do the sscanf() on the next line.

This code is not really desigined to handle partial writes where *offp is non-zero and the "buf" is preserved and re-used between writes. Just ban partial writes and replace the simple_write_to_buffer() with copy_from_user().

index b7bf3f863d79..5ee0afa621a9 100644
@@ -367,14 +367,16 @@ static ssize_t tool_fn_write(struct tool_ctx *tc,
 	u64 bits;
 	int n;
 
+	if (*offp)
+		return 0;
+
 	buf = kmalloc(size + 1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
-	ret = simple_write_to_buffer(buf, size, offp, ubuf, size);
-	if (ret < 0) {
+	if (copy_from_user(buf, ubuf, size)) {
 		kfree(buf);
-		return ret;
+		return -EFAULT;
 	}
 
 	buf[size] = 0;