linux-kernel - Re: [PATCH] net: bmac: Fix stack corruption panic in bmac

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Date:   Mon, 18 May 2020 09:06:59 +0800
From:   Jeremy Kerr <jk@...abs.org>
To:     Finn Thain <fthain@...egraphics.com.au>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Paul Mackerras <paulus@...ba.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Stan Johnson <userm57@...oo.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] net: bmac: Fix stack corruption panic in bmac_probe()

Hi Finn,

> This fixes an old bug recently revealed by CONFIG_STACKPROTECTOR.

Good catch. I'm not sure about the fix though. That variable ('addr')
should be a ethernet hardware address; I'm surprised we're accessing
past the 6th byte. The culprit seems to be this, where 'ea' is the
address buffer:

   static void
   bmac_get_station_address(struct net_device *dev, unsigned char *ea)
   {
        int i;
        unsigned short data;

        for (i = 0; i < 6; i++)
                {
                        reset_and_select_srom(dev);
                        data = read_srom(dev, i + EnetAddressOffset/2, SROMAddressBits);
                        ea[2*i]   = bitrev8(data & 0x0ff);
                        ea[2*i+1] = bitrev8((data >> 8) & 0x0ff);
                }
   }

- where it looks like the condition on that for-loop is wrong; we're
reading two bytes at a time there.

Can you try the attached patch?

Ben/Paul - any thoughts?

Cheers,


Jeremy

-----

>From 141b20bcbdb3ad7c166b83b4ea61f3521d0a0679 Mon Sep 17 00:00:00 2001
From: Jeremy Kerr <jk@...abs.org>
Date: Mon, 18 May 2020 08:54:25 +0800
Subject: [PATCH] net: bmac: Fix read of MAC address from ROM

In bmac_get_station_address, We're reading two bytes at a time from ROM,
but we do that six times, resulting in 12 bytes of read & writes. This
means we will write off the end of the six-byte destination buffer.

This change fixes the for-loop to only read/write six bytes.

Based on a proposed fix from Finn Thain <fthain@...egraphics.com.au>.

Signed-off-by: Jeremy Kerr <jk@...abs.org>
Reported-by: Stan Johnson <userm57@...oo.com>
Reported-by: Finn Thain <fthain@...egraphics.com.au>
---
 drivers/net/ethernet/apple/bmac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/apple/bmac.c b/drivers/net/ethernet/apple/bmac.c
index a58185b1d8bf..3e3711b60d01 100644
--- a/drivers/net/ethernet/apple/bmac.c
+++ b/drivers/net/ethernet/apple/bmac.c
@@ -1182,7 +1182,7 @@ bmac_get_station_address(struct net_device *dev, unsigned char *ea)
        int i;
        unsigned short data;
 
-       for (i = 0; i < 6; i++)
+       for (i = 0; i < 3; i++)
                {
                        reset_and_select_srom(dev);
                        data = read_srom(dev, i + EnetAddressOffset/2, SROMAddressBits);
-- 
2.17.1