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
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
-
