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Subject[PATCH 2/6] Drivers: hv: vmbus: Avoid double fetch of msgtype in vmbus_on_msg_dpc()
Date
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 <juvazq@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
---
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
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