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Subject[PATCH 3/6] Drivers: hv: vmbus: Avoid double fetch of payload_size in vmbus_on_msg_dpc()
Date
vmbus_on_msg_dpc() double fetches from payload_size.  The double fetch
can lead to a buffer overflow when (mem)copying the hv_message object.
Avoid the double fetch by saving the value of payload_size 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 | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 82b23baa446d7..0e39f1d6182e9 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1056,6 +1056,7 @@ void vmbus_on_msg_dpc(unsigned long data)
void *page_addr = hv_cpu->synic_message_page;
struct hv_message *msg = (struct hv_message *)page_addr +
VMBUS_MESSAGE_SINT;
+ __u8 payload_size = msg->header.payload_size;
struct vmbus_channel_message_header *hdr;
enum vmbus_channel_message_type msgtype;
const struct vmbus_channel_message_table_entry *entry;
@@ -1089,9 +1090,8 @@ void vmbus_on_msg_dpc(unsigned long data)
goto msg_handled;
}

- if (msg->header.payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT) {
- WARN_ONCE(1, "payload size is too large (%d)\n",
- msg->header.payload_size);
+ if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT) {
+ WARN_ONCE(1, "payload size is too large (%d)\n", payload_size);
goto msg_handled;
}

@@ -1100,21 +1100,18 @@ void vmbus_on_msg_dpc(unsigned long data)
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",
- msgtype, msg->header.payload_size);
+ if (payload_size < entry->min_payload_len) {
+ WARN_ONCE(1, "message too short: msgtype=%d len=%d\n", msgtype, payload_size);
goto msg_handled;
}

if (entry->handler_type == VMHT_BLOCKING) {
- ctx = kmalloc(sizeof(*ctx) + msg->header.payload_size,
- GFP_ATOMIC);
+ ctx = kmalloc(sizeof(*ctx) + payload_size, GFP_ATOMIC);
if (ctx == NULL)
return;

INIT_WORK(&ctx->work, vmbus_onmessage_work);
- memcpy(&ctx->msg, msg, sizeof(msg->header) +
- msg->header.payload_size);
+ memcpy(&ctx->msg, msg, sizeof(msg->header) + payload_size);

/*
* The host can generate a rescind message while we
--
2.25.1
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