linux-kernel - Re: [PATCH v5 06/14] iommufd: Add IOMMUFD_OBJ_VEVENTQ and IOMMUFD_CMD_VEVENTQ

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

Message-ID: <20250110174842.GI396083@nvidia.com>
Date: Fri, 10 Jan 2025 13:48:42 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, corbet@....net, will@...nel.org, joro@...tes.org,
	suravee.suthikulpanit@....com, robin.murphy@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com, shuah@...nel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
	eric.auger@...hat.com, jean-philippe@...aro.org, mdf@...nel.org,
	mshavit@...gle.com, shameerali.kolothum.thodi@...wei.com,
	smostafa@...gle.com, ddutile@...hat.com, yi.l.liu@...el.com,
	patches@...ts.linux.dev
Subject: Re: [PATCH v5 06/14] iommufd: Add IOMMUFD_OBJ_VEVENTQ and
 IOMMUFD_CMD_VEVENTQ_ALLOC

On Tue, Jan 07, 2025 at 09:10:09AM -0800, Nicolin Chen wrote:

> +static ssize_t iommufd_veventq_fops_read(struct iommufd_eventq *eventq,
> +					 char __user *buf, size_t count,
> +					 loff_t *ppos)
> +{
> +	size_t done = 0;
> +	int rc = 0;
> +
> +	if (*ppos)
> +		return -ESPIPE;
> +
> +	mutex_lock(&eventq->mutex);
> +	while (!list_empty(&eventq->deliver) && count > done) {
> +		struct iommufd_vevent *cur = list_first_entry(
> +			&eventq->deliver, struct iommufd_vevent, node);
> +
> +		if (cur->data_len > count - done)
> +			break;
> +
> +		if (copy_to_user(buf + done, cur->event_data, cur->data_len)) {
> +			rc = -EFAULT;
> +			break;
> +		}

Now that I look at this more closely, the fault path this is copied
from is not great.

This copy_to_user() can block while waiting on a page fault, possibily
for a long time. While blocked the mutex is held and we can't add more
entries to the list.

That will cause the shared IRQ handler in the iommu driver to back up,
which would cause a global DOS.

This probably wants to be organized to look more like

while (itm = eventq_get_next_item(eventq)) {
   if (..) {
       eventq_restore_failed_item(eventq);
       return -1;
   }
}

Where the next_item would just be a simple spinlock across the linked
list manipulation.

Jason