Re: [PATCH 1/3] scsi: qedf: do not touch __user pointer in qedf_dbg_stop_io_on_error_cmd_read() directly

[Oleksandr Natalenko <oleksandr@redhat.com>]

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Hello.

On pátek 28. července 2023 17:23:25 CEST David Laight wrote:
> From: Oleksandr Natalenko
> > Sent: 28 July 2023 07:58
> > 
> > The qedf_dbg_stop_io_on_error_cmd_read() function invokes sprintf()
> > directly on a __user pointer, which may crash the kernel.
> > 
> > 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.
> > 
> > Fixes: 61d8658b4a ("scsi: qedf: Add QLogic FastLinQ offload FCoE driver framework.")
> ...
> > diff --git a/drivers/scsi/qedf/qedf_debugfs.c b/drivers/scsi/qedf/qedf_debugfs.c
> > index a3ed681c8ce3f..4d1b99569d490 100644
> > --- a/drivers/scsi/qedf/qedf_debugfs.c
> > +++ b/drivers/scsi/qedf/qedf_debugfs.c
> > @@ -185,18 +185,17 @@ qedf_dbg_stop_io_on_error_cmd_read(struct file *filp, char __user *buffer,
> >  				   size_t count, loff_t *ppos)
> >  {
> >  	int cnt;
> > +	char cbuf[7];
> >  	struct qedf_dbg_ctx *qedf_dbg =
> >  				(struct qedf_dbg_ctx *)filp->private_data;
> >  	struct qedf_ctx *qedf = container_of(qedf_dbg,
> >  	    struct qedf_ctx, dbg_ctx);
> > 
> >  	QEDF_INFO(qedf_dbg, QEDF_LOG_DEBUGFS, "entered\n");
> > -	cnt = sprintf(buffer, "%s\n",
> > +	cnt = sprintf(cbuf, "%s\n",
> >  	    qedf->stop_io_on_error ? "true" : "false");
> 
> You've made cbuf[] exactly just big enough.
> If anyone breathes on this code it could overflow.
> You really should use scnprintf() for safety.

OK, I'll do scnprintf(cbuf, sizeof(cbuf), ...) in the next version of the submission.

Thanks.

> > 
> > -	cnt = min_t(int, count, cnt - *ppos);
> > -	*ppos += cnt;
> > -	return cnt;
> > +	return simple_read_from_buffer(buffer, count, ppos, cbuf, cnt);
> 
> Or just:
> 	if (gedf->stop_on_error)
> 		return simple_read_from_buffer(buffer, count, ppos, "true\n", 5);
> 	return simple_read_from_buffer(buffer, count, ppos, "false\n", 6);
> 
> 	David
> 
> 	
> >  }
> > 
> >  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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