linux-kernel - mmap abuses in drm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 19 Dec 2006 12:41:08 +0100
From:	Christoph Hellwig <hch@....de>
To:	airlied@...ux.ie, dri-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: mmap abuses in drm

Folks, could someone explain what the heck is going on here:

static int i830_map_buffer(drm_buf_t * buf, struct file *filp)
{
	drm_file_t *priv = filp->private_data;
	drm_device_t *dev = priv->head->dev;
	drm_i830_buf_priv_t *buf_priv = buf->dev_private;
	drm_i830_private_t *dev_priv = dev->dev_private;
	const struct file_operations *old_fops;
	unsigned long virtual;
	int retcode = 0;

	if (buf_priv->currently_mapped == I830_BUF_MAPPED)
		return -EINVAL;

	down_write(&current->mm->mmap_sem);
	old_fops = filp->f_op;
	filp->f_op = &i830_buffer_fops;
	dev_priv->mmap_buffer = buf;
	virtual = do_mmap(filp, 0, buf->total, PROT_READ | PROT_WRITE,
			  MAP_SHARED, buf->bus_address);
	dev_priv->mmap_buffer = NULL;
	filp->f_op = old_fops;
	if (IS_ERR((void *)virtual)) {	/* ugh */
		/* Real error */
		DRM_ERROR("mmap error\n");
		retcode = PTR_ERR((void *)virtual);
		buf_priv->virtual = NULL;
	} else {
		buf_priv->virtual = (void __user *)virtual;
	}
	up_write(&current->mm->mmap_sem);

	return retcode;
}

(and same crap in i810_dma.c aswell)

Overriding the file operations just for mmap is for one thing racy
as hell and for another very fragile as the mmap and nopage routines
have to agree closely on what to do.

Even further why in hell do you call do_mmap from a driver?  Mapping
memory into userspace from anything but syscall dedicated to it is
surely a desaster waiting to happen.

Is there any chance we can get rid of this crap (and similar stuff in
drm_bufs.c) as part of the memory manager overhaul?  Long-term I'd
like to get rid of the do_mmap(_pgoff) export to avoid that people
introduce similar braindamage again.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/