From: Vladis Dronov vdronov@redhat.com

commit 13054abbaa4f1fd4e6f3b4b63439ec033b4c8035 upstream.

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 v3: use __set_current_state() instead of set_current_state()

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1669187 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@redhat.com Reviewed-by: Oleg Nesterov oleg@redhat.com Signed-off-by: Benjamin Tissoires benjamin.tissoires@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [groeck: backport to v4.9.y] Signed-off-by: Guenter Roeck linux@roeck-us.net --- This patch is marked v4.18+, but commit 717adfdaf147 is marked for stable and found its way into all stable releases. Therefore, this patch is needed in older stable releases as well. This patch only applies to v4.9.y.

Note: The offending patch is in v4.4.y as well, but trying to apply the fix to v4.4.y was messy, so I gave up on it.

Copying patch author and reviewers to make sure I didn't miss anything.

drivers/hid/hid-debug.c | 121 ++++++++++++++++++---------------------------- include/linux/hid-debug.h | 9 ++-- 2 files changed, 51 insertions(+), 79 deletions(-)

diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c index 29423691c105..07833e4add78 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.h> #include <linux/export.h> #include <linux/slab.h> @@ -659,17 +660,12 @@ 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); @@ -720,8 +716,7 @@ 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);

@@ -1086,8 +1081,8 @@ static int hid_debug_events_open(struct inode *inode, struct file *file) goto out; }

- if (!(list->hid_debug_buf = kzalloc(sizeof(char) * 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; } @@ -1107,77 +1102,57 @@ 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 (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 (!list->hdev || !list->hdev->debug) { - ret = -EIO; - set_current_state(TASK_RUNNING); - goto out; - } + if (signal_pending(current)) { + ret = -ERESTARTSYS; + break; + }

- /* allow O_NONBLOCK from other threads */ - mutex_unlock(&list->read_mutex); - schedule(); - mutex_lock(&list->read_mutex); - set_current_state(TASK_INTERRUPTIBLE); + /* 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; }

- set_current_state(TASK_RUNNING); - remove_wait_queue(&list->hdev->debug_wait, &wait); + /* allow O_NONBLOCK from other threads */ + mutex_unlock(&list->read_mutex); + schedule(); + mutex_lock(&list->read_mutex); + set_current_state(TASK_INTERRUPTIBLE); }

- if (ret) - goto out; + __set_current_state(TASK_RUNNING); + remove_wait_queue(&list->hdev->debug_wait, &wait);

- /* pass the ringbuffer contents to userspace */ -copy_rest: - if (list->tail == list->head) + if (ret) 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; @@ -1187,8 +1162,7 @@ static unsigned int 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 POLLIN | POLLRDNORM; if (!list->hdev->debug) return POLLERR | POLLHUP; @@ -1203,7 +1177,7 @@ 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; @@ -1254,4 +1228,3 @@ 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..2d6100edf204 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); @@ -37,11 +40,8 @@ void hid_debug_init(void); void hid_debug_exit(void); 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 -