linux-kernel - [char-misc-next 1/3] mei: validate the message header only in first fragment.

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Date:   Mon, 12 Jun 2017 12:15:55 +0300
From:   Tomas Winkler <tomas.winkler@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Alexander Usyskin <alexander.usyskin@...el.com>,
        linux-kernel@...r.kernel.org,
        Tomas Winkler <tomas.winkler@...el.com>
Subject: [char-misc-next 1/3] mei: validate the message header only in first fragment.

RX message header is received in the first fragment of
the message and saved side and it is not modified after that,
we don't need to validate it upon each fragment.

Signed-off-by: Tomas Winkler <tomas.winkler@...el.com>
---
 drivers/misc/mei/interrupt.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/drivers/misc/mei/interrupt.c b/drivers/misc/mei/interrupt.c
index c14e35201721..b0b8f18a85e3 100644
--- a/drivers/misc/mei/interrupt.c
+++ b/drivers/misc/mei/interrupt.c
@@ -235,6 +235,17 @@ static inline bool hdr_is_fixed(struct mei_msg_hdr *mei_hdr)
 	return mei_hdr->host_addr == 0 && mei_hdr->me_addr != 0;
 }
 
+static inline int hdr_is_valid(u32 msg_hdr)
+{
+	struct mei_msg_hdr *mei_hdr;
+
+	mei_hdr = (struct mei_msg_hdr *)&msg_hdr;
+	if (!msg_hdr || mei_hdr->reserved)
+		return -EBADMSG;
+
+	return 0;
+}
+
 /**
  * mei_irq_read_handler - bottom half read routine after ISR to
  * handle the read processing.
@@ -256,17 +267,18 @@ int mei_irq_read_handler(struct mei_device *dev,
 		dev->rd_msg_hdr = mei_read_hdr(dev);
 		(*slots)--;
 		dev_dbg(dev->dev, "slots =%08x.\n", *slots);
-	}
-	mei_hdr = (struct mei_msg_hdr *) &dev->rd_msg_hdr;
-	dev_dbg(dev->dev, MEI_HDR_FMT, MEI_HDR_PRM(mei_hdr));
 
-	if (mei_hdr->reserved || !dev->rd_msg_hdr) {
-		dev_err(dev->dev, "corrupted message header 0x%08X\n",
+		ret = hdr_is_valid(dev->rd_msg_hdr);
+		if (ret) {
+			dev_err(dev->dev, "corrupted message header 0x%08X\n",
 				dev->rd_msg_hdr);
-		ret = -EBADMSG;
-		goto end;
+			goto end;
+		}
 	}
 
+	mei_hdr = (struct mei_msg_hdr *)&dev->rd_msg_hdr;
+	dev_dbg(dev->dev, MEI_HDR_FMT, MEI_HDR_PRM(mei_hdr));
+
 	if (mei_slots2data(*slots) < mei_hdr->length) {
 		dev_err(dev->dev, "less data available than length=%08x.\n",
 				*slots);
-- 
2.9.4