Re: [PATCH] blktrace: fix a bug in blk_msg_write()

[Ingo Molnar]

* Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:

> On Fri, Apr 03 2009, Ingo Molnar wrote:
> > 
> > * Li Zefan <lizf@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > > ---
> > >  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@xxxxxxxxxx>
> > 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@xxxxxxxxxxx>
> 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@xxxxxxxxxxx>

Sure, i've picked up Carl's version of the fix instead, it dates 
back to early February!

( Li Zefan's fix was a tiny notch cleaner - i picked that cleanup up
  on top of Carl's patch separately. )

Thanks,

	Ingo
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