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

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Date:	Fri, 3 Apr 2009 13:17:41 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Jens Axboe <jens.axboe@...cle.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>
Subject: Re: [PATCH] blktrace: fix a bug in blk_msg_write()


* 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'

	Ingo
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