CVE-2023-52564

En el kernel de Linux, se resolvió la siguiente vulnerabilidad: Revertir "tty: n_gsm: fix UAF in gsm_cleanup_mux" Esto revierte el commit 9b9c8195f3f0d74a826077fc1c01b9ee74907239. el commit anterior se revierte porque no resolvió el problema original. gsm_cleanup_mux() intenta liberar los ttys virtuales llamando a gsm_dlci_release() para cada DLCI disponible. Allí, se llama a dlci_put() para disminuir el contador de referencia para el DLCI a través de tty_port_put() que finalmente llama a gsm_dlci_free(). Esto ya borra el puntero que se está verificando en gsm_cleanup_mux() antes de llamar a gsm_dlci_release(). Por lo tanto, no es necesario borrar este puntero en gsm_cleanup_mux() como se hizo en el commit revertida. el commit introduce una desreferencia de puntero nulo: ? __die+0x1f/0x70 ? page_fault_oops+0x156/0x420? search_exception_tables+0x37/0x50? fixup_exception+0x21/0x310? exc_page_fault+0x69/0x150? asm_exc_page_fault+0x26/0x30? tty_port_put+0x19/0xa0 gsmtty_cleanup+0x29/0x80 [n_gsm] release_one_tty+0x37/0xe0 proceso_one_work+0x1e6/0x3e0 trabajador_thread+0x4c/0x3d0 ? __pfx_worker_thread+0x10/0x10 kthread+0xe1/0x110 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x2f/0x50 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1b/0x30 El problema real es que nada protege a dlci_put() de ser llamado varias veces mientras el controlador tty se activó pero aún no terminó de llamar a gsm_dlci_free().

In the Linux kernel, the following vulnerability has been resolved: Revert "tty: n_gsm: fix UAF in gsm_cleanup_mux" This reverts commit 9b9c8195f3f0d74a826077fc1c01b9ee74907239. The commit above is reverted as it did not solve the original issue. gsm_cleanup_mux() tries to free up the virtual ttys by calling gsm_dlci_release() for each available DLCI. There, dlci_put() is called to decrease the reference counter for the DLCI via tty_port_put() which finally calls gsm_dlci_free(). This already clears the pointer which is being checked in gsm_cleanup_mux() before calling gsm_dlci_release(). Therefore, it is not necessary to clear this pointer in gsm_cleanup_mux() as done in the reverted commit. The commit introduces a null pointer dereference: <TASK> ? __die+0x1f/0x70 ? page_fault_oops+0x156/0x420 ? search_exception_tables+0x37/0x50 ? fixup_exception+0x21/0x310 ? exc_page_fault+0x69/0x150 ? asm_exc_page_fault+0x26/0x30 ? tty_port_put+0x19/0xa0 gsmtty_cleanup+0x29/0x80 [n_gsm] release_one_tty+0x37/0xe0 process_one_work+0x1e6/0x3e0 worker_thread+0x4c/0x3d0 ? __pfx_worker_thread+0x10/0x10 kthread+0xe1/0x110 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x2f/0x50 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1b/0x30 </TASK> The actual issue is that nothing guards dlci_put() from being called multiple times while the tty driver was triggered but did not yet finished calling gsm_dlci_free().