From 90c1a74271ce4667d16eeca575dfa78a6c7d465c Mon Sep 17 00:00:00 2001
From: Michael Hanselmann <public@hansmi.ch>
Date: Thu, 13 Dec 2018 22:37:06 +0000
Subject: [PATCH] usb-mtp: Limit filename to object information size
The filename length in MTP metadata is specified by the guest. By
trusting it directly it'd theoretically be possible to get the host to
write memory parts outside the filename buffer into a filename. In
practice though there are usually NUL bytes stopping the string
operations.
Also use the opportunity to not assign the filename member twice.
Signed-off-by: Michael Hanselmann <public@hansmi.ch>
Message-id: ab70659d8d5c580bdf150a5f7d5cc60c8e374ffc.1544740018.git.public@hansmi.ch
[ kraxel: codestyle fix: break a long line ]
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
hw/usb/dev-mtp.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c
index 36c43b8c20..6098005cd4 100644
--- a/hw/usb/dev-mtp.c
+++ b/hw/usb/dev-mtp.c
@@ -1710,7 +1710,7 @@ free:
s->write_pending = false;
}
-static void usb_mtp_write_metadata(MTPState *s)
+static void usb_mtp_write_metadata(MTPState *s, uint64_t dlen)
{
MTPData *d = s->data_out;
ObjectInfo *dataset = (ObjectInfo *)d->data;
@@ -1722,7 +1722,9 @@ static void usb_mtp_write_metadata(MTPState *s)
assert(!s->write_pending);
assert(p != NULL);
- filename = utf16_to_str(dataset->length, dataset->filename);
+ filename = utf16_to_str(MIN(dataset->length,
+ dlen - offsetof(ObjectInfo, filename)),
+ dataset->filename);
if (strchr(filename, '/')) {
usb_mtp_queue_result(s, RES_PARAMETER_NOT_SUPPORTED, d->trans,
@@ -1738,7 +1740,6 @@ static void usb_mtp_write_metadata(MTPState *s)
s->dataset.filename = filename;
s->dataset.format = dataset->format;
s->dataset.size = dataset->size;
- s->dataset.filename = filename;
s->write_pending = true;
if (s->dataset.format == FMT_ASSOCIATION) {
@@ -1807,7 +1808,7 @@ static void usb_mtp_get_data(MTPState *s, mtp_container *container,
if (d->offset == d->length) {
/* The operation might have already failed */
if (!s->result) {
- usb_mtp_write_metadata(s);
+ usb_mtp_write_metadata(s, dlen);
}
usb_mtp_data_free(s->data_out);
s->data_out = NULL;