linux-kernel - AW: [PATCH] ISDN cmx: Avoid potential NULL deref in dsp_cmx_send

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Message-ID: <B16317F2B1592B4492FC414114171CE604B08AEA@FLBVEXCH01.versatel.local>
Date:	Mon, 20 Dec 2010 12:26:23 +0100
From:	"Andreas.Eversberg" <Andreas.Eversberg@...satel.de>
To:	"Jesper Juhl" <jj@...osbits.net>,
	"Karsten Keil" <isdn@...ux-pingi.de>
Cc:	"David S. Miller" <davem@...emloft.net>,
	"Julia Lawall" <julia@...u.dk>, "Tejun Heo" <tj@...nel.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: AW: [PATCH] ISDN cmx: Avoid potential NULL deref in dsp_cmx_send_member() and shrink code size.

hi jesper,

thanx for finding the bug. i think the right solution to solve the problem would be:

                if (dsp->conf && dsp->conf->software && dsp->conf->hardware)
                        tx_data_only = 1;
->              if (dsp->echo.software && dsp->echo.hardware)
                        tx_data_only = 1;

this is how it looks in the 'socket' branch of mISDN git respository. it has been fixed already. but i cannot tell in which commit. my current head is this commit:
commit 45a51eed1c554a4891b48b88c270f4f95bd21df0

what branch do you use? 

regards,

andreas


-----Ursprüngliche Nachricht-----
Von: Jesper Juhl [mailto:jj@...osbits.net] 
Gesendet: Samstag, 18. Dezember 2010 23:34
An: Karsten Keil
Cc: David S. Miller; Julia Lawall; Tejun Heo; netdev@...r.kernel.org; linux-kernel@...r.kernel.org; Andreas Eversberg
Betreff: [PATCH] ISDN cmx: Avoid potential NULL deref in dsp_cmx_send_member() and shrink code size.

Hi there,

In drivers/isdn/mISDN/dsp_cmx.c::dsp_cmx_send_member() we currently have 
this code:

           if (dsp->conf && dsp->conf->software && dsp->conf->hardware)
                   tx_data_only = 1;
           if (dsp->conf->software && dsp->echo.hardware)
                   tx_data_only = 1;

The first line implies that 'dsp->conf' may be NULL. If it is, then the 
third line will dereference a NULL pointer.

This patch reworks the code so that we avoid the potential NULL deref.
It also has the added benefit that the object file size shrinks a bit.

before:
   text    data     bss     dec     hex filename
  18840     112    5784   24736    60a0 drivers/isdn/mISDN/dsp_cmx.o
after:
   text    data     bss     dec     hex filename
  18816     112    5776   24704    6080 drivers/isdn/mISDN/dsp_cmx.o


Signed-off-by: Jesper Juhl <jj@...osbits.net>
---
 dsp_cmx.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

 compile tested only

diff --git a/drivers/isdn/mISDN/dsp_cmx.c b/drivers/isdn/mISDN/dsp_cmx.c
index 76d9e67..f76f595 100644
--- a/drivers/isdn/mISDN/dsp_cmx.c
+++ b/drivers/isdn/mISDN/dsp_cmx.c
@@ -1326,10 +1326,9 @@ dsp_cmx_send_member(struct dsp *dsp, int len, s32 *c, int members)
 			dsp->last_tx = 0;
 			return;
 		}
-		if (dsp->conf && dsp->conf->software && dsp->conf->hardware)
-			tx_data_only = 1;
-		if (dsp->conf->software && dsp->echo.hardware)
-			tx_data_only = 1;
+		if (dsp->conf && dsp->conf->software)
+			if (dsp->conf->hardware || dsp->echo.hardware)
+				tx_data_only = 1;
 	}
 
 #ifdef CMX_DEBUG



-- 
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