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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Daniel Rosenberg <drosen@google.com>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Jiri Kosina <jkosina@suse.cz>
Subject: [PATCH 4.9 39/52] HID: debug: check length before copy_to_user()
Date:   Tue, 10 Jul 2018 20:25:07 +0200
Message-Id: <20180710182452.938266092@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Daniel Rosenberg <drosen@google.com>

commit 717adfdaf14704fd3ec7fa2c04520c0723247eac upstream.

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

Cc: stable@vger.kernel.org
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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
@@ -1152,6 +1152,8 @@ 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;
@@ -1161,6 +1163,8 @@ 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;
@@ -1168,7 +1172,9 @@ copy_rest:
 			}
 			list->head = 0;
 			ret += len;
-			goto copy_rest;
+			count -= len;
+			if (count > 0)
+				goto copy_rest;
 		}
 
 	}