RE: [PATCH 3/6] Drivers: hv: vmbus: Avoid double fetch of payload_size in vmbus_on_msg_dpc()
From: Michael Kelley <hidden>
Date: 2020-12-06 17:15:08
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From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Wednesday, November 18, 2020 6:37 AM
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.
Similar comment here about providing some brief context in the commit message on the problem that we are guarding against by removing the double fetch. I could see combining this patch with the previous one since the motivation and pattern of the changes are exactly the same, just for two different fields. Michael
quoted hunk ↗ jump to hunk
Reported-by: Juan Vazquez <redacted> 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