linux-kernel - Re: [PATCH] pps: fix poll support

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] [day] [month] [year] [list]

Message-ID: <2738fe1c-4dc7-4d8c-ac8a-f32e5b3277c3@enneenne.com>
Date: Mon, 3 Mar 2025 12:53:52 +0100
From: Rodolfo Giometti <giometti@...eenne.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Denis OSTERLAND-HEIM <denis.osterland@...hl.com>, stable@...r.kernel.org
Subject: Re: [PATCH] pps: fix poll support

On 03/03/25 09:02, Denis OSTERLAND-HEIM wrote:
> [BUG]
> A user space program that calls select/poll get always an immediate data
> ready-to-read response. As a result the intended use to wait until next
> data becomes ready does not work.
> 
> User space snippet:
> 
>      struct pollfd pollfd = {
>        .fd = open("/dev/pps0", O_RDONLY),
>        .events = POLLIN|POLLERR,
>        .revents = 0 };
>      while(1) {
>        poll(&pollfd, 1, 2000/*ms*/); // returns immediate, but should wait
>        if(revents & EPOLLIN) { // always true
>          struct pps_fdata fdata;
>          memset(&fdata, 0, sizeof(memdata));
>          ioctl(PPS_FETCH, &fdata); // currently fetches data at max speed
>        }
>      }
> 
> [CAUSE]
> pps_cdev_poll() returns unconditionally EPOLLIN.
> 
> [FIX]
> Remember the last fetch event counter and compare this value in
> pps_cdev_poll() with most recent event counter
> and return 0 if they are equal.
> 
> Signed-off-by: Denis OSTERLAND-HEIM <denis.osterland@...hl.com>
> Co-developed-by: Rodolfo Giometti <giometti@...eenne.com>
> Signed-off-by: Rodolfo Giometti <giometti@...eenne.com>

Acked-by: Rodolfo Giometti <giometti@...eenne.com>

If needed. :)

> Fixes: eae9d2ba0cfc ("LinuxPPS: core support")
> CC: stable@...r.linux.org # 5.4+
> ---
>   drivers/pps/pps.c          | 11 +++++++++--
>   include/linux/pps_kernel.h |  1 +
>   2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
> index 6a02245ea35f..9463232af8d2 100644
> --- a/drivers/pps/pps.c
> +++ b/drivers/pps/pps.c
> @@ -41,6 +41,9 @@ static __poll_t pps_cdev_poll(struct file *file, poll_table *wait)
>   
>   	poll_wait(file, &pps->queue, wait);
>   
> +	if (pps->last_fetched_ev == pps->last_ev)
> +		return 0;
> +
>   	return EPOLLIN | EPOLLRDNORM;
>   }
>   
> @@ -186,9 +189,11 @@ static long pps_cdev_ioctl(struct file *file,
>   		if (err)
>   			return err;
>   
> -		/* Return the fetched timestamp */
> +		/* Return the fetched timestamp and save last fetched event  */
>   		spin_lock_irq(&pps->lock);
>   
> +		pps->last_fetched_ev = pps->last_ev;
> +
>   		fdata.info.assert_sequence = pps->assert_sequence;
>   		fdata.info.clear_sequence = pps->clear_sequence;
>   		fdata.info.assert_tu = pps->assert_tu;
> @@ -272,9 +277,11 @@ static long pps_cdev_compat_ioctl(struct file *file,
>   		if (err)
>   			return err;
>   
> -		/* Return the fetched timestamp */
> +		/* Return the fetched timestamp and save last fetched event  */
>   		spin_lock_irq(&pps->lock);
>   
> +		pps->last_fetched_ev = pps->last_ev;
> +
>   		compat.info.assert_sequence = pps->assert_sequence;
>   		compat.info.clear_sequence = pps->clear_sequence;
>   		compat.info.current_mode = pps->current_mode;
> diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h
> index c7abce28ed29..aab0aebb529e 100644
> --- a/include/linux/pps_kernel.h
> +++ b/include/linux/pps_kernel.h
> @@ -52,6 +52,7 @@ struct pps_device {
>   	int current_mode;			/* PPS mode at event time */
>   
>   	unsigned int last_ev;			/* last PPS event id */
> +	unsigned int last_fetched_ev;		/* last fetched PPS event id */
>   	wait_queue_head_t queue;		/* PPS event queue */
>   
>   	unsigned int id;			/* PPS source unique ID */

-- 
GNU/Linux Solutions                  e-mail: giometti@...eenne.com
Linux Device Driver                          giometti@...ux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming