linux-kernel - [PATCH] HID: debug: check length before copy_to

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Message-Id: <20180702235937.111619-1-drosen@google.com>
Date:   Mon,  2 Jul 2018 16:59:37 -0700
From:   Daniel Rosenberg <drosen@...gle.com>
To:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Daniel Rosenberg <drosen@...gle.com>, stable@...r.kernel.org
Subject: [PATCH] HID: debug: check length before copy_to_user()

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

Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
Cc: stable@...r.kernel.org
---
 drivers/hid/hid-debug.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
index 8469b6964ff64..b48100236df89 100644
--- a/drivers/hid/hid-debug.c
+++ b/drivers/hid/hid-debug.c
@@ -1154,6 +1154,8 @@ static ssize_t hid_debug_events_read(struct file *file, char __user *buffer,
 			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;
@@ -1163,6 +1165,8 @@ static ssize_t hid_debug_events_read(struct file *file, char __user *buffer,
 			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;
@@ -1170,7 +1174,9 @@ static ssize_t hid_debug_events_read(struct file *file, char __user *buffer,
 			}
 			list->head = 0;
 			ret += len;
-			goto copy_rest;
+			count -= len;
+			if (count > 0)
+				goto copy_rest;
 		}
 
 	}
-- 
2.18.0.399.gad0ab374a1-goog