linux-kernel - Re: [PATCH 2/3] scsi: qedf: do not touch __user pointer in qedf_dbg_debug_cmd

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Message-ID: <5955796.lOV4Wx5bFT@redhat.com>
Date:   Mon, 31 Jul 2023 10:11:33 +0200
From:   Oleksandr Natalenko <oleksandr@...hat.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     David Laight <David.Laight@...lab.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        Saurav Kashyap <skashyap@...vell.com>,
        Johannes Thumshirn <Johannes.Thumshirn@....com>,
        "GR-QLogic-Storage-Upstream@...vell.com" 
        <GR-QLogic-Storage-Upstream@...vell.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Jozef Bacik <jobacik@...hat.com>,
        Laurence Oberman <loberman@...hat.com>,
        Rob Evers <revers@...hat.com>
Subject: Re: [PATCH 2/3] scsi: qedf: do not touch __user pointer in
 qedf_dbg_debug_cmd_read() directly

Hello/

On pátek 28. července 2023 17:26:11 CEST David Laight wrote:
> From: Oleksandr Natalenko
> > Sent: 28 July 2023 07:58
> > 
> > The qedf_dbg_debug_cmd_read() function invokes sprintf()
> > directly on a __user pointer, which may crash the kernel.
>                                       ^^^ will

I don't think it is 100% guaranteed, but for sure this is not a correct behaviour.

> > 
> > Avoid doing that by using a small on-stack buffer for sprintf()
> > and then calling simple_read_from_buffer() which does a proper
> > copy_to_user() call.
> ...
> > diff --git a/drivers/scsi/qedf/qedf_debugfs.c b/drivers/scsi/qedf/qedf_debugfs.c
> > index 4d1b99569d490..f910af0029a2c 100644
> > --- a/drivers/scsi/qedf/qedf_debugfs.c
> > +++ b/drivers/scsi/qedf/qedf_debugfs.c
> > @@ -138,15 +138,14 @@ qedf_dbg_debug_cmd_read(struct file *filp, char __user *buffer, size_t count,
> >  			loff_t *ppos)
> >  {
> >  	int cnt;
> > +	char cbuf[35];
> 
> Why 35?
> I pick a multiple of 8 that if 'enough.

OK, I overestimated this, it should have been 27, but I'll make it 32 to be a multiple of 8.

Thanks.

> >  	struct qedf_dbg_ctx *qedf_dbg =
> >  				(struct qedf_dbg_ctx *)filp->private_data;
> > 
> >  	QEDF_INFO(qedf_dbg, QEDF_LOG_DEBUGFS, "debug mask=0x%x\n", qedf_debug);
> > -	cnt = sprintf(buffer, "debug mask = 0x%x\n", qedf_debug);
> > +	cnt = sprintf(cbuf, "debug mask = 0x%x\n", qedf_debug);
> 
> Use scnprintf() to be sure it doesn't overflow.
> Much safer if someone does a quick update or copies the code.
> 
> 	David
> 
> > 
> > -	cnt = min_t(int, count, cnt - *ppos);
> > -	*ppos += cnt;
> > -	return cnt;
> > +	return simple_read_from_buffer(buffer, count, ppos, cbuf, cnt);
> >  }
> > 
> >  static ssize_t
> > --
> > 2.41.0
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 
> 


-- 
Oleksandr Natalenko (post-factum)
Principal Software Maintenance Engineer
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