6.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: Daniel Starke daniel.starke@siemens.com
commit 29346e217b8ab8a52889b88f00b268278d6b7668 upstream.
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().
Fixes: 9b9c8195f3f0 ("tty: n_gsm: fix UAF in gsm_cleanup_mux") Cc: stable stable@kernel.org Signed-off-by: Daniel Starke daniel.starke@siemens.com Link: https://lore.kernel.org/r/20230914051507.3240-1-daniel.starke@siemens.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/n_gsm.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -3071,10 +3071,8 @@ static void gsm_cleanup_mux(struct gsm_m gsm->has_devices = false; } for (i = NUM_DLCI - 1; i >= 0; i--) - if (gsm->dlci[i]) { + if (gsm->dlci[i]) gsm_dlci_release(gsm->dlci[i]); - gsm->dlci[i] = NULL; - } mutex_unlock(&gsm->mutex); /* Now wipe the queues */ tty_ldisc_flush(gsm->tty);