linux-kernel - [PATCH 3.16 013/132] media: wl128x: prevent two potential buffer overflows

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Message-ID: <lsq.1568989415.650123541@decadent.org.uk>
Date:   Fri, 20 Sep 2019 15:23:35 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Hans Verkuil" <hverkuil-cisco@...all.nl>,
        "Dan Carpenter" <dan.carpenter@...cle.com>,
        "Mauro Carvalho Chehab" <mchehab+samsung@...nel.org>
Subject: [PATCH 3.16 013/132] media: wl128x: prevent two potential buffer
 overflows

3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@...cle.com>

commit 9c2ccc324b3a6cbc865ab8b3e1a09e93d3c8ade9 upstream.

Smatch marks skb->data as untrusted so it warns that "evt_hdr->dlen"
can copy up to 255 bytes and we only have room for two bytes.  Even
if this comes from the firmware and we trust it, the new policy
generally is just to fix it as kernel hardenning.

I can't test this code so I tried to be very conservative.  I considered
not allowing "evt_hdr->dlen == 1" because it doesn't initialize the
whole variable but in the end I decided to allow it and manually
initialized "asic_id" and "asic_ver" to zero.

Fixes: e8454ff7b9a4 ("[media] drivers:media:radio: wl128x: FM Driver Common sources")

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/drivers/media/radio/wl128x/fmdrv_common.c
+++ b/drivers/media/radio/wl128x/fmdrv_common.c
@@ -494,7 +494,8 @@ int fmc_send_cmd(struct fmdev *fmdev, u8
 		return -EIO;
 	}
 	/* Send response data to caller */
-	if (response != NULL && response_len != NULL && evt_hdr->dlen) {
+	if (response != NULL && response_len != NULL && evt_hdr->dlen &&
+	    evt_hdr->dlen <= payload_len) {
 		/* Skip header info and copy only response data */
 		skb_pull(skb, sizeof(struct fm_event_msg_hdr));
 		memcpy(response, skb->data, evt_hdr->dlen);
@@ -590,6 +591,8 @@ static void fm_irq_handle_flag_getcmd_re
 		return;
 
 	fm_evt_hdr = (void *)skb->data;
+	if (fm_evt_hdr->dlen > sizeof(fmdev->irq_info.flag))
+		return;
 
 	/* Skip header info and copy only response data */
 	skb_pull(skb, sizeof(struct fm_event_msg_hdr));
@@ -1318,7 +1321,8 @@ static int load_default_rx_configuration
 /* Does FM power on sequence */
 static int fm_power_up(struct fmdev *fmdev, u8 mode)
 {
-	u16 payload, asic_id, asic_ver;
+	u16 payload;
+	__be16 asic_id = 0, asic_ver = 0;
 	int resp_len, ret;
 	u8 fw_name[50];