Re: [PATCH v2] HID: debug: fix the ring buffer implementation
From: Benjamin Tissoires
Date: Mon Jan 28 2019 - 04:15:09 EST
On Sat, Jan 26, 2019 at 6:07 PM Vladis Dronov <vdronov@xxxxxxxxxx> wrote:
>
> Ring buffer implementation in hid_debug_event() and hid_debug_events_read()
> is strange allowing lost or corrupted data. After commit 717adfdaf147
> ("HID: debug: check length before copy_to_user()") it is possible to enter
> an infinite loop in hid_debug_events_read() by providing 0 as count, this
> locks up a system. Fix this by rewriting the ring buffer implementation
> with kfifo and simplify the code.
>
> This fixes CVE-2019-3819.
>
> v2: fix an execution logic and add a comment
Thanks for the respin.
v2 looks good to me.
Oleg, can you provide some feedback before I push this?
Cheers,
Benjamin
>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1669187
> Cc: stable@xxxxxxxxxxxxxxx # v4.18+
> Fixes: cd667ce24796 ("HID: use debugfs for events/reports dumping")
> Fixes: 717adfdaf147 ("HID: debug: check length before copy_to_user()")
> Signed-off-by: Vladis Dronov <vdronov@xxxxxxxxxx>
> ---
> drivers/hid/hid-debug.c | 116 ++++++++++++++------------------------
> include/linux/hid-debug.h | 9 ++-
> 2 files changed, 47 insertions(+), 78 deletions(-)
>
> diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
> index c530476edba6..08870c909268 100644
> --- a/drivers/hid/hid-debug.c
> +++ b/drivers/hid/hid-debug.c
> @@ -30,6 +30,7 @@
>
> #include <linux/debugfs.h>
> #include <linux/seq_file.h>
> +#include <linux/kfifo.h>
> #include <linux/sched/signal.h>
> #include <linux/export.h>
> #include <linux/slab.h>
> @@ -661,17 +662,12 @@ EXPORT_SYMBOL_GPL(hid_dump_device);
> /* enqueue string to 'events' ring buffer */
> void hid_debug_event(struct hid_device *hdev, char *buf)
> {
> - unsigned i;
> struct hid_debug_list *list;
> unsigned long flags;
>
> spin_lock_irqsave(&hdev->debug_list_lock, flags);
> - list_for_each_entry(list, &hdev->debug_list, node) {
> - for (i = 0; buf[i]; i++)
> - list->hid_debug_buf[(list->tail + i) % HID_DEBUG_BUFSIZE] =
> - buf[i];
> - list->tail = (list->tail + i) % HID_DEBUG_BUFSIZE;
> - }
> + list_for_each_entry(list, &hdev->debug_list, node)
> + kfifo_in(&list->hid_debug_fifo, buf, strlen(buf));
> spin_unlock_irqrestore(&hdev->debug_list_lock, flags);
>
> wake_up_interruptible(&hdev->debug_wait);
> @@ -722,8 +718,7 @@ void hid_dump_input(struct hid_device *hdev, struct hid_usage *usage, __s32 valu
> hid_debug_event(hdev, buf);
>
> kfree(buf);
> - wake_up_interruptible(&hdev->debug_wait);
> -
> + wake_up_interruptible(&hdev->debug_wait);
> }
> EXPORT_SYMBOL_GPL(hid_dump_input);
>
> @@ -1083,8 +1078,8 @@ static int hid_debug_events_open(struct inode *inode, struct file *file)
> goto out;
> }
>
> - if (!(list->hid_debug_buf = kzalloc(HID_DEBUG_BUFSIZE, GFP_KERNEL))) {
> - err = -ENOMEM;
> + err = kfifo_alloc(&list->hid_debug_fifo, HID_DEBUG_FIFOSIZE, GFP_KERNEL);
> + if (err) {
> kfree(list);
> goto out;
> }
> @@ -1104,77 +1099,57 @@ static ssize_t hid_debug_events_read(struct file *file, char __user *buffer,
> size_t count, loff_t *ppos)
> {
> struct hid_debug_list *list = file->private_data;
> - int ret = 0, len;
> + int ret = 0, copied;
> DECLARE_WAITQUEUE(wait, current);
>
> mutex_lock(&list->read_mutex);
> - while (ret == 0) {
> - if (list->head == list->tail) {
> - add_wait_queue(&list->hdev->debug_wait, &wait);
> - set_current_state(TASK_INTERRUPTIBLE);
> -
> - while (list->head == list->tail) {
> - if (file->f_flags & O_NONBLOCK) {
> - ret = -EAGAIN;
> - break;
> - }
> - if (signal_pending(current)) {
> - ret = -ERESTARTSYS;
> - break;
> - }
> -
> - if (!list->hdev || !list->hdev->debug) {
> - ret = -EIO;
> - set_current_state(TASK_RUNNING);
> - goto out;
> - }
> -
> - /* allow O_NONBLOCK from other threads */
> - mutex_unlock(&list->read_mutex);
> - schedule();
> - mutex_lock(&list->read_mutex);
> - set_current_state(TASK_INTERRUPTIBLE);
> - }
> -
> - set_current_state(TASK_RUNNING);
> - remove_wait_queue(&list->hdev->debug_wait, &wait);
> - }
> -
> - if (ret)
> - goto out;
> + if (kfifo_is_empty(&list->hid_debug_fifo)) {
> + add_wait_queue(&list->hdev->debug_wait, &wait);
> + set_current_state(TASK_INTERRUPTIBLE);
> +
> + while (kfifo_is_empty(&list->hid_debug_fifo)) {
> + if (file->f_flags & O_NONBLOCK) {
> + ret = -EAGAIN;
> + break;
> + }
> +
> + if (signal_pending(current)) {
> + ret = -ERESTARTSYS;
> + break;
> + }
> +
> + /* if list->hdev is NULL we cannot remove_wait_queue().
> + * if list->hdev->debug is 0 then hid_debug_unregister()
> + * was already called and list->hdev is being destroyed.
> + * if we add remove_wait_queue() here we can hit a race.
> + */
> + if (!list->hdev || !list->hdev->debug) {
> + ret = -EIO;
> + set_current_state(TASK_RUNNING);
> + goto out;
> + }
> +
> + /* allow O_NONBLOCK from other threads */
> + mutex_unlock(&list->read_mutex);
> + schedule();
> + mutex_lock(&list->read_mutex);
> + set_current_state(TASK_INTERRUPTIBLE);
> + }
> +
> + set_current_state(TASK_RUNNING);
> + remove_wait_queue(&list->hdev->debug_wait, &wait);
> +
> + if (ret)
> + goto out;
> + }
>
> - /* pass the ringbuffer contents to userspace */
> -copy_rest:
> - if (list->tail == list->head)
> - goto out;
> - if (list->tail > list->head) {
> - len = list->tail - list->head;
> - if (len > count)
> - len = count;
> -
> - if (copy_to_user(buffer + ret, &list->hid_debug_buf[list->head], len)) {
> - ret = -EFAULT;
> - goto out;
> - }
> - ret += len;
> - list->head += len;
> - } else {
> - len = HID_DEBUG_BUFSIZE - list->head;
> - if (len > count)
> - len = count;
> -
> - if (copy_to_user(buffer, &list->hid_debug_buf[list->head], len)) {
> - ret = -EFAULT;
> - goto out;
> - }
> - list->head = 0;
> - ret += len;
> - count -= len;
> - if (count > 0)
> - goto copy_rest;
> - }
> -
> - }
> + /* pass the fifo content to userspace, locking is not needed with only
> + * one concurrent reader and one concurrent writer
> + */
> + ret = kfifo_to_user(&list->hid_debug_fifo, buffer, count, &copied);
> + if (ret)
> + goto out;
> + ret = copied;
> out:
> mutex_unlock(&list->read_mutex);
> return ret;
> @@ -1185,7 +1160,7 @@ static __poll_t hid_debug_events_poll(struct file *file, poll_table *wait)
> struct hid_debug_list *list = file->private_data;
>
> poll_wait(file, &list->hdev->debug_wait, wait);
> - if (list->head != list->tail)
> + if (!kfifo_is_empty(&list->hid_debug_fifo))
> return EPOLLIN | EPOLLRDNORM;
> if (!list->hdev->debug)
> return EPOLLERR | EPOLLHUP;
> @@ -1200,7 +1175,7 @@ static int hid_debug_events_release(struct inode *inode, struct file *file)
> spin_lock_irqsave(&list->hdev->debug_list_lock, flags);
> list_del(&list->node);
> spin_unlock_irqrestore(&list->hdev->debug_list_lock, flags);
> - kfree(list->hid_debug_buf);
> + kfifo_free(&list->hid_debug_fifo);
> kfree(list);
>
> return 0;
> @@ -1246,4 +1221,3 @@ void hid_debug_exit(void)
> {
> debugfs_remove_recursive(hid_debug_root);
> }
> -
> diff --git a/include/linux/hid-debug.h b/include/linux/hid-debug.h
> index 8663f216c563..e7a7c92aaf09 100644
> --- a/include/linux/hid-debug.h
> +++ b/include/linux/hid-debug.h
> @@ -24,7 +24,10 @@
>
> #ifdef CONFIG_DEBUG_FS
>
> +#include <linux/kfifo.h>
> +
> #define HID_DEBUG_BUFSIZE 512
> +#define HID_DEBUG_FIFOSIZE 512
>
> void hid_dump_input(struct hid_device *, struct hid_usage *, __s32);
> void hid_dump_report(struct hid_device *, int , u8 *, int);
> @@ -38,10 +41,7 @@ void hid_debug_event(struct hid_device *, char *);
> void hid_debug_event(struct hid_device *, char *);
>
> -
> struct hid_debug_list {
> - char *hid_debug_buf;
> - int head;
> - int tail;
> + DECLARE_KFIFO_PTR(hid_debug_fifo, char);
> struct fasync_struct *fasync;
> struct hid_device *hdev;
> struct list_head node;
> @@ -64,4 +64,3 @@ struct hid_debug_list {
> #endif
>
> #endif
> -