[question] potential race between capinc_tty_init & capi_release

From: Saubhik Mukherjee
Date: Tue Aug 17 2021 - 05:13:33 EST

In drivers/isdn/capi/capi.c, based on the output of a static analysis tool, we found the possibility of the following race condition:

In capi_init, register_chrdev registers file operations callbacks, capi_fops. Then capinc_tty_init is executed.

Simultaneously the following chain of calls can occur (after a successful capi_open call).

capi_release -> capincci_free -> capincci_free_minor -> capiminor_free -> tty_unregister_device

tty_unregister_device reads capinc_tty_driver, which might not have been initialized at this point. So, we have a race between capi_release and capinc_tty_init.

If this is a possible race scenario, maybe moving register_chrdev after capinc_tty_init could fix it. But I am not sure if this will break something else. Please let me know if this is a potential race and can be fixed as mentioned.

Since this is based on a static analysis tool, this is not tested.