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authorTzung-Bi Shih <tzungbi@google.com>2022-02-09 13:11:30 +0800
committerBenson Leung <bleung@chromium.org>2022-03-31 16:56:48 -0700
commit0e8eb5e8acbad19ac2e1856b2fb2320184299b33 (patch)
tree4282e4cde184c01f828c95640c8ad6e1e94d0abf /drivers/platform
parenteabd9a3807e17e211690e6c40f1405b427b64c48 (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>
Diffstat (limited to 'drivers/platform')
-rw-r--r--drivers/platform/chrome/cros_ec_debugfs.c12
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);