kern/155658: [amr] [patch] amr_ioctl(): call of malloc() causes memory corruption and panic

John Baldwin jhb at
Fri Apr 20 12:50:10 UTC 2012

The following reply was made to PR kern/155658; it has been noted by GNATS.

From: John Baldwin <jhb at>
To: Andreas Longwitz <longwitz at>
Cc: bug-followup at,
 scottl at
Subject: Re: kern/155658: [amr] [patch] amr_ioctl(): call of malloc() causes memory corruption and panic
Date: Fri, 20 Apr 2012 08:13:50 -0400

 On Thursday, April 19, 2012 4:12:50 pm Andreas Longwitz wrote:
 > John,
 > I did several tests with your patch in 8.2 and everything works fine, if
 > I use the binary version of megarc with the patch included described in
 > ports/137938.
 > The original megarc sends amr_ioctl's with length 12868 (e.g. the first
 > ioctl of the command "megarc -ctlrinfo -a0") and your patch calls the
 > controller with real_length=16384, but the controller returns 25412
 > Bytes. This happens all the time on nearly every megarc command, I think
 > this is a program error in megarc, he uses user_cmd=0xa104 with buffer
 > length 12868, but the firmware of the controller replies with 25412
 > bytes. So we have memory corruption of 25412 - 16384 = 9026 bytes. The
 > patch in ports/137938 changes the lenght field in megarc from 12868 to
 > 25412 to avoid this problem. A line like
 >        if( len == 12868 ) len = 25412;
 > would solve this problem in the driver. I did not find any other static
 > problems of this type.
 > Another story are dynamic problems. When the controller is very busy, I
 > see sometimes 1KB bytes returned from the controller, when lenght is
 > much lower. This problem is handled by your patch in all cases.
 > Andreas Longwitz
 Ah, ok.  I think we should just make the minimum buffer size 32k which
 should workaround this.  I've updated the patch at the same URL:
 John Baldwin

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