linux-kernel - Re: [PATCH] blktrace: fix a bug in blk_msg

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Message-ID: <20090403125956.GA25027@elte.hu>
Date:	Fri, 3 Apr 2009 14:59:56 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Alan D. Brunelle" <alan.brunelle@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Carl Henrik Lunde <chlunde@...g.uio.no>
Subject: Re: [PATCH] blktrace: fix a bug in blk_msg_write()


* Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Jens Axboe <jens.axboe@...cle.com> wrote:
> 
> > On Fri, Apr 03 2009, Ingo Molnar wrote:
> > > 
> > > * Li Zefan <lizf@...fujitsu.com> wrote:
> > > 
> > > > This is another long-standing bug.
> > > >
> > > > ================
> > > >
> > > >
> > > >  (console 1)
> > > >  # echo -n 'a' > /sys/kernel/debug/block/sda/msg
> > > >  (console 2)
> > > >  # blktrace -d /dev/sda -a pc -o - | blkparse -i -
> > > >   8,0    0        0     0.000000000     0  m   N a??????????????????@...???
> > > >
> > > > We should terminate the msg buffer with '\0'.
> > > >
> > > > Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> > > > ---
> > > >  kernel/trace/blktrace.c |    5 +++--
> > > >  1 files changed, 3 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> > > > index c0ef70d..2bf341f 100644
> > > > --- a/kernel/trace/blktrace.c
> > > > +++ b/kernel/trace/blktrace.c
> > > > @@ -327,10 +327,10 @@ static ssize_t blk_msg_write(struct file *filp, const char __user *buffer,
> > > >  	char *msg;
> > > >  	struct blk_trace *bt;
> > > >
> > > > -	if (count > BLK_TN_MAX_MSG)
> > > > +	if (count >= BLK_TN_MAX_MSG)
> > > >  		return -EINVAL;
> > > >
> > > > -	msg = kmalloc(count, GFP_KERNEL);
> > > > +	msg = kmalloc(count + 1, GFP_KERNEL);
> > > >  	if (msg == NULL)
> > > >  		return -ENOMEM;
> > > >
> > > > @@ -338,6 +338,7 @@ static ssize_t blk_msg_write(struct file *filp, const char __user *buffer,
> > > >  		kfree(msg);
> > > >  		return -EFAULT;
> > > >  	}
> > > > +	msg[count] = '\0';
> > > >
> > > >  	bt = filp->private_data;
> > > >  	__trace_note_message(bt, "%s", msg);
> > > 
> > > Nice fix!
> > > 
> > > Jens, do you ack this and should i add a Cc: <stable@...nel.org>
> > > backporting tag?
> > > 
> > > This fix applies fine to v2.6.29 after:
> > > 
> > >    sed 's/kernel\/trace\/blktrace.c/block\/blktrace.c'
> > 
> > This is identical to the following patch from Carl Henrik Lunde, which
> > he just ported to -tip. It has existed before, as a patch to 2.6.29-git,
> > but was unfortunately dropped.
> > 
> > So is this a coincidence? If not, Carl Henrik Lunde should be credited.
> > 
> > >From f116bce73e04d01614fd28ea678e0953cc321155 Mon Sep 17 00:00:00 2001
> > From: Carl Henrik Lunde <chlunde@...g.uio.no>
> > Date: Wed, 25 Mar 2009 14:23:16 +0100
> > Subject: [PATCH] blktrace: NUL-terminate user space messages
> > 
> > Make sure messages from user space are NUL-terminated strings,
> > otherwise we could dump random memory to the block trace file.
> > Additionally, I've limited the message to BLK_TN_MAX_MSG-1 characters,
> > because the last character would be stripped by vscnprintf anyway.
> > 
> > Signed-off-by: Carl Henrik Lunde <chlunde@...g.uio.no>
> 
> Sure, i've picked up Carl's version of the fix instead, it dates 
> back to early February!

I've also checked the linux-btrace archives a few months back and 
nothing else seems to be missing - are you aware of any other 
missing items?

	Ingo
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