From: Tzung-Bi Shih tzungbi@google.com
[ Upstream commit 0e8eb5e8acbad19ac2e1856b2fb2320184299b33 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/platform/chrome/cros_ec_debugfs.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/drivers/platform/chrome/cros_ec_debugfs.c b/drivers/platform/chrome/cros_ec_debugfs.c index 6ae484989d1f..c4b57e1df192 100644 --- a/drivers/platform/chrome/cros_ec_debugfs.c +++ b/drivers/platform/chrome/cros_ec_debugfs.c @@ -26,6 +26,9 @@
#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. * @@ -34,7 +37,6 @@ * @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 */ @@ -45,7 +47,6 @@ 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; @@ -108,7 +109,7 @@ 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); @@ -142,7 +143,7 @@ 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; @@ -174,7 +175,7 @@ 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, @@ -359,7 +360,6 @@ 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);