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[82.51.6.75]) by smtp.gmail.com with ESMTPSA id w10sm34795307wra.34.2020.11.18.06.37.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Nov 2020 06:37:41 -0800 (PST) From: "Andrea Parri (Microsoft)" To: linux-kernel@vger.kernel.org Cc: "K . Y . Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , linux-hyperv@vger.kernel.org, Michael Kelley , Juan Vazquez , Saruhan Karademir , "Andrea Parri (Microsoft)" Subject: [PATCH 2/6] Drivers: hv: vmbus: Avoid double fetch of msgtype in vmbus_on_msg_dpc() Date: Wed, 18 Nov 2020 15:36:45 +0100 Message-Id: <20201118143649.108465-3-parri.andrea@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201118143649.108465-1-parri.andrea@gmail.com> References: <20201118143649.108465-1-parri.andrea@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Signed-off-by: Andrea Parri (Microsoft) --- 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