linux-kernel - [PATCH 3.16 129/131] HID: debug: check length before copy_to

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Message-ID: <lsq.1538257387.70998880@decadent.org.uk>
Date:   Sat, 29 Sep 2018 22:43:07 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jiri Kosina" <jkosina@...e.cz>,
        "Daniel Rosenberg" <drosen@...gle.com>,
        "Benjamin Tissoires" <benjamin.tissoires@...hat.com>
Subject: [PATCH 3.16 129/131] HID: debug: check length before copy_to_user()

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

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

From: Daniel Rosenberg <drosen@...gle.com>

commit 717adfdaf14704fd3ec7fa2c04520c0723247eac upstream.

If our length is greater than the size of the buffer, we
overflow the buffer

Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/hid/hid-debug.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/hid/hid-debug.c
+++ b/drivers/hid/hid-debug.c
@@ -1150,6 +1150,8 @@ copy_rest:
 			goto out;
 		if (list->tail > list->head) {
 			len = list->tail - list->head;
+			if (len > count)
+				len = count;
 
 			if (copy_to_user(buffer + ret, &list->hid_debug_buf[list->head], len)) {
 				ret = -EFAULT;
@@ -1159,6 +1161,8 @@ copy_rest:
 			list->head += len;
 		} else {
 			len = HID_DEBUG_BUFSIZE - list->head;
+			if (len > count)
+				len = count;
 
 			if (copy_to_user(buffer, &list->hid_debug_buf[list->head], len)) {
 				ret = -EFAULT;
@@ -1166,7 +1170,9 @@ copy_rest:
 			}
 			list->head = 0;
 			ret += len;
-			goto copy_rest;
+			count -= len;
+			if (count > 0)
+				goto copy_rest;
 		}
 
 	}