diff options
| author | Tzung-Bi Shih <tzungbi@google.com> | 2022-02-09 13:11:30 +0800 |
|---|---|---|
| committer | Benson Leung <bleung@chromium.org> | 2022-03-31 16:56:48 -0700 |
| commit | 0e8eb5e8acbad19ac2e1856b2fb2320184299b33 (patch) | |
| tree | 4282e4cde184c01f828c95640c8ad6e1e94d0abf | |
| parent | eabd9a3807e17e211690e6c40f1405b427b64c48 (diff) | |
platform/chrome: cros_ec_debugfs: detach log reader wq from devm
Debugfs console_log uses devm memory (e.g. debug_info in
cros_ec_console_log_poll()). However, lifecycles of device and debugfs
are independent. An use-after-free issue is observed if userland
program operates the debugfs after the memory has been freed.
The call trace:
do_raw_spin_lock
_raw_spin_lock_irqsave
remove_wait_queue
ep_unregister_pollwait
ep_remove
do_epoll_ctl
A Python example to reproduce the issue:
... import select
... p = select.epoll()
... f = open('/sys/kernel/debug/cros_scp/console_log')
... p.register(f, select.POLLIN)
... p.poll(1)
[(4, 1)] # 4=fd, 1=select.POLLIN
[ shutdown cros_scp at the point ]
... p.poll(1)
[(4, 16)] # 4=fd, 16=select.POLLHUP
... p.unregister(f)
An use-after-free issue raises here. It called epoll_ctl with
EPOLL_CTL_DEL which in turn to use the workqueue in the devm (i.e.
log_wq).
Detaches log reader's workqueue from devm to make sure it is persistent
even if the device has been removed.
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Reviewed-by: Guenter Roeck <groeck@google.com>
Link: https://lore.kernel.org/r/20220209051130.386175-1-tzungbi@google.com
Signed-off-by: Benson Leung <bleung@chromium.org>
| -rw-r--r-- | drivers/platform/chrome/cros_ec_debugfs.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/drivers/platform/chrome/cros_ec_debugfs.c b/drivers/platform/chrome/cros_ec_debugfs.c index 272c89837d74..0dbceee87a4b 100644 --- a/drivers/platform/chrome/cros_ec_debugfs.c +++ b/drivers/platform/chrome/cros_ec_debugfs.c @@ -25,6 +25,9 @@ #define CIRC_ADD(idx, size, value) (((idx) + (value)) & ((size) - 1)) +/* waitqueue for log readers */ +static DECLARE_WAIT_QUEUE_HEAD(cros_ec_debugfs_log_wq); + /** * struct cros_ec_debugfs - EC debugging information. * @@ -33,7 +36,6 @@ * @log_buffer: circular buffer for console log information * @read_msg: preallocated EC command and buffer to read console log * @log_mutex: mutex to protect circular buffer - * @log_wq: waitqueue for log readers * @log_poll_work: recurring task to poll EC for new console log data * @panicinfo_blob: panicinfo debugfs blob */ @@ -44,7 +46,6 @@ struct cros_ec_debugfs { struct circ_buf log_buffer; struct cros_ec_command *read_msg; struct mutex log_mutex; - wait_queue_head_t log_wq; struct delayed_work log_poll_work; /* EC panicinfo */ struct debugfs_blob_wrapper panicinfo_blob; @@ -107,7 +108,7 @@ static void cros_ec_console_log_work(struct work_struct *__work) buf_space--; } - wake_up(&debug_info->log_wq); + wake_up(&cros_ec_debugfs_log_wq); } mutex_unlock(&debug_info->log_mutex); @@ -141,7 +142,7 @@ static ssize_t cros_ec_console_log_read(struct file *file, char __user *buf, mutex_unlock(&debug_info->log_mutex); - ret = wait_event_interruptible(debug_info->log_wq, + ret = wait_event_interruptible(cros_ec_debugfs_log_wq, CIRC_CNT(cb->head, cb->tail, LOG_SIZE)); if (ret < 0) return ret; @@ -173,7 +174,7 @@ static __poll_t cros_ec_console_log_poll(struct file *file, struct cros_ec_debugfs *debug_info = file->private_data; __poll_t mask = 0; - poll_wait(file, &debug_info->log_wq, wait); + poll_wait(file, &cros_ec_debugfs_log_wq, wait); mutex_lock(&debug_info->log_mutex); if (CIRC_CNT(debug_info->log_buffer.head, @@ -377,7 +378,6 @@ static int cros_ec_create_console_log(struct cros_ec_debugfs *debug_info) debug_info->log_buffer.tail = 0; mutex_init(&debug_info->log_mutex); - init_waitqueue_head(&debug_info->log_wq); debugfs_create_file("console_log", S_IFREG | 0444, debug_info->dir, debug_info, &cros_ec_console_log_fops); |