vmbus_on_msg_dpc() double fetches from msgtype. The double fetch can
lead to an out-of-bound access when accessing the channel_message_table
array. In turn, the use of the out-of-bound entry could lead to code
execution primitive (entry->message_handler()). Avoid the double fetch
by saving the value of msgtype into a local variable.
Reported-by: Juan Vazquez <[email protected]>
Signed-off-by: Andrea Parri (Microsoft) <[email protected]>
---
drivers/hv/vmbus_drv.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 0a2711aa63a15..82b23baa446d7 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1057,6 +1057,7 @@ void vmbus_on_msg_dpc(unsigned long data)
struct hv_message *msg = (struct hv_message *)page_addr +
VMBUS_MESSAGE_SINT;
struct vmbus_channel_message_header *hdr;
+ enum vmbus_channel_message_type msgtype;
const struct vmbus_channel_message_table_entry *entry;
struct onmessage_work_context *ctx;
u32 message_type = msg->header.message_type;
@@ -1072,12 +1073,19 @@ void vmbus_on_msg_dpc(unsigned long data)
/* no msg */
return;
+ /*
+ * The hv_message object is in memory shared with the host. The host
+ * could erroneously or maliciously modify such object. Make sure to
+ * validate its fields and avoid double fetches whenever feasible.
+ */
+
hdr = (struct vmbus_channel_message_header *)msg->u.payload;
+ msgtype = hdr->msgtype;
trace_vmbus_on_msg_dpc(hdr);
- if (hdr->msgtype >= CHANNELMSG_COUNT) {
- WARN_ONCE(1, "unknown msgtype=%d\n", hdr->msgtype);
+ if (msgtype >= CHANNELMSG_COUNT) {
+ WARN_ONCE(1, "unknown msgtype=%d\n", msgtype);
goto msg_handled;
}
@@ -1087,14 +1095,14 @@ void vmbus_on_msg_dpc(unsigned long data)
goto msg_handled;
}
- entry = &channel_message_table[hdr->msgtype];
+ entry = &channel_message_table[msgtype];
if (!entry->message_handler)
goto msg_handled;
if (msg->header.payload_size < entry->min_payload_len) {
WARN_ONCE(1, "message too short: msgtype=%d len=%d\n",
- hdr->msgtype, msg->header.payload_size);
+ msgtype, msg->header.payload_size);
goto msg_handled;
}
@@ -1115,7 +1123,7 @@ void vmbus_on_msg_dpc(unsigned long data)
* by offer_in_progress and by channel_mutex. See also the
* inline comments in vmbus_onoffer_rescind().
*/
- switch (hdr->msgtype) {
+ switch (msgtype) {
case CHANNELMSG_RESCIND_CHANNELOFFER:
/*
* If we are handling the rescind message;
--
2.25.1
On Wed, Dec 02, 2020 at 10:22:09AM +0100, Andrea Parri (Microsoft) wrote:
> vmbus_on_msg_dpc() double fetches from msgtype. The double fetch can
> lead to an out-of-bound access when accessing the channel_message_table
> array. In turn, the use of the out-of-bound entry could lead to code
> execution primitive (entry->message_handler()). Avoid the double fetch
> by saving the value of msgtype into a local variable.
>
> Reported-by: Juan Vazquez <[email protected]>
> Signed-off-by: Andrea Parri (Microsoft) <[email protected]>
> ---
> drivers/hv/vmbus_drv.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 0a2711aa63a15..82b23baa446d7 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1057,6 +1057,7 @@ void vmbus_on_msg_dpc(unsigned long data)
> struct hv_message *msg = (struct hv_message *)page_addr +
> VMBUS_MESSAGE_SINT;
> struct vmbus_channel_message_header *hdr;
> + enum vmbus_channel_message_type msgtype;
> const struct vmbus_channel_message_table_entry *entry;
> struct onmessage_work_context *ctx;
> u32 message_type = msg->header.message_type;
> @@ -1072,12 +1073,19 @@ void vmbus_on_msg_dpc(unsigned long data)
> /* no msg */
> return;
>
> + /*
> + * The hv_message object is in memory shared with the host. The host
> + * could erroneously or maliciously modify such object. Make sure to
> + * validate its fields and avoid double fetches whenever feasible.
> + */
> +
> hdr = (struct vmbus_channel_message_header *)msg->u.payload;
> + msgtype = hdr->msgtype;
Should READ_ONCE be used here?
Wei.
> > @@ -1072,12 +1073,19 @@ void vmbus_on_msg_dpc(unsigned long data)
> > /* no msg */
> > return;
> >
> > + /*
> > + * The hv_message object is in memory shared with the host. The host
> > + * could erroneously or maliciously modify such object. Make sure to
> > + * validate its fields and avoid double fetches whenever feasible.
> > + */
> > +
> > hdr = (struct vmbus_channel_message_header *)msg->u.payload;
> > + msgtype = hdr->msgtype;
>
> Should READ_ONCE be used here?
I think it should. Thank you for pointing this out.
Andrea
On Wed, Dec 02, 2020 at 02:37:16PM +0100, Andrea Parri wrote:
> > > @@ -1072,12 +1073,19 @@ void vmbus_on_msg_dpc(unsigned long data)
> > > /* no msg */
> > > return;
> > >
> > > + /*
> > > + * The hv_message object is in memory shared with the host. The host
> > > + * could erroneously or maliciously modify such object. Make sure to
> > > + * validate its fields and avoid double fetches whenever feasible.
> > > + */
> > > +
> > > hdr = (struct vmbus_channel_message_header *)msg->u.payload;
> > > + msgtype = hdr->msgtype;
> >
> > Should READ_ONCE be used here?
>
> I think it should. Thank you for pointing this out.
Glad I can help.
The same comment applies to other patches as well, of course.
Wei.
>
> Andrea
On Wed, Dec 02, 2020 at 01:40:04PM +0000, Wei Liu wrote:
> On Wed, Dec 02, 2020 at 02:37:16PM +0100, Andrea Parri wrote:
> > > > @@ -1072,12 +1073,19 @@ void vmbus_on_msg_dpc(unsigned long data)
> > > > /* no msg */
> > > > return;
> > > >
> > > > + /*
> > > > + * The hv_message object is in memory shared with the host. The host
> > > > + * could erroneously or maliciously modify such object. Make sure to
> > > > + * validate its fields and avoid double fetches whenever feasible.
> > > > + */
> > > > +
> > > > hdr = (struct vmbus_channel_message_header *)msg->u.payload;
> > > > + msgtype = hdr->msgtype;
> > >
> > > Should READ_ONCE be used here?
> >
> > I think it should. Thank you for pointing this out.
>
> Glad I can help.
>
> The same comment applies to other patches as well, of course.
(As discussed offline/for reference:) I can spot a similar case in
patch #3; however, #4 is supposed to make that access 'non-shared'.
I should probably just squash patches #3 and #4; I'll try to do so
in v3...
Thanks,
Andrea