5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Daniel Starke <daniel.starke@xxxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Daniel Starke <daniel.starke@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230914051507.3240-1-daniel.starke@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
@@ -2412,10 +2412,8 @@ 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);
