[PATCH 5.9 194/255] speakup: Fix clearing selection in safe context

Greg Kroah-Hartman
2020-11-17T13:44:42Z

From: Samuel Thibault <samuel.thibault@ens-lyon.org>

commit 640969a69ca4dd2ac025fe873c6bf25eba8f11b3 upstream.

speakup_cut() calls speakup_clear_selection() which calls console_lock.
Problem is: speakup_cut() is called from a keyboard interrupt
context. This would hang if speakup_cut is pressed while the console
lock is unfortunately already held.

We can however as well just defer calling clear_selection() until the
already-deferred set_selection_kernel() call.

This was spotted by the lock hardener:

Possible unsafe locking scenario:\x0a
CPU0
----
lock(console_lock);
<Interrupt>
lock(console_lock);
\x0a *** DEADLOCK ***\x0a
[...]
Call Trace:
<IRQ>
dump_stack+0xc2/0x11a
print_usage_bug.cold+0x3e0/0x4b1
mark_lock+0xd95/0x1390
? print_irq_inversion_bug+0xa0/0xa0
__lock_acquire+0x21eb/0x5730
? __kasan_check_read+0x11/0x20
? check_chain_key+0x215/0x5e0
? register_lock_class+0x1580/0x1580
? lock_downgrade+0x7a0/0x7a0
? __rwlock_init+0x140/0x140
lock_acquire+0x13f/0x370
? speakup_clear_selection+0xe/0x20 [speakup]
console_lock+0x33/0x50
? speakup_clear_selection+0xe/0x20 [speakup]
speakup_clear_selection+0xe/0x20 [speakup]
speakup_cut+0x19e/0x4b0 [speakup]
keyboard_notifier_call+0x1f04/0x4a40 [speakup]
? read_all_doc+0x240/0x240 [speakup]
notifier_call_chain+0xbf/0x130
__atomic_notifier_call_chain+0x80/0x130
atomic_notifier_call_chain+0x16/0x20
kbd_event+0x7d7/0x3b20
? k_pad+0x850/0x850
? sysrq_filter+0x450/0xd40
input_to_handler+0x362/0x4b0
? rcu_read_lock_sched_held+0xe0/0xe0
input_pass_values+0x408/0x5a0
? __rwlock_init+0x140/0x140
? lock_acquire+0x13f/0x370
input_handle_event+0x70e/0x1380
input_event+0x67/0x90
atkbd_interrupt+0xe62/0x1d4e [atkbd]
? __kasan_check_write+0x14/0x20
? atkbd_event_work+0x130/0x130 [atkbd]
? _raw_spin_lock_irqsave+0x26/0x70
serio_interrupt+0x93/0x120 [serio]
i8042_interrupt+0x232/0x510 [i8042]
? rcu_read_lock_bh_held+0xd0/0xd0
? handle_irq_event+0xa5/0x13a
? i8042_remove+0x1f0/0x1f0 [i8042]
__handle_irq_event_percpu+0xe6/0x6c0
handle_irq_event_percpu+0x71/0x150
? __handle_irq_event_percpu+0x6c0/0x6c0
? __kasan_check_read+0x11/0x20
? do_raw_spin_unlock+0x5c/0x240
handle_irq_event+0xad/0x13a
handle_edge_irq+0x233/0xa90
do_IRQ+0x10b/0x310
common_interrupt+0xf/0xf
</IRQ>

Cc: stable@vger.kernel.org
Reported-by: Jookia <contact@jookia.org>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20201107233310.7iisvaozpiqj3yvy@function
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/accessibility/speakup/main.c | 1 -
drivers/accessibility/speakup/selection.c | 11 ++++-------
drivers/accessibility/speakup/speakup.h | 1 -
3 files changed, 4 insertions(+), 9 deletions(-)

--- a/drivers/accessibility/speakup/main.c
+++ b/drivers/accessibility/speakup/main.c
@@ -357,7 +357,6 @@ static void speakup_cut(struct vc_data *
mark_cut_flag = 0;
synth_printf("%s\n", spk_msg_get(MSG_CUT));

- speakup_clear_selection();
ret = speakup_set_selection(tty);

switch (ret) {
--- a/drivers/accessibility/speakup/selection.c
+++ b/drivers/accessibility/speakup/selection.c
@@ -22,13 +22,6 @@ struct speakup_selection_work {
struct tty_struct *tty;
};

-void speakup_clear_selection(void)
-{
- console_lock();
- clear_selection();
- console_unlock();
-}
-
static void __speakup_set_selection(struct work_struct *work)
{
struct speakup_selection_work *ssw =
@@ -51,6 +44,10 @@ static void __speakup_set_selection(stru
goto unref;
}

+ console_lock();
+ clear_selection();
+ console_unlock();
+
set_selection_kernel(&sel, tty);

unref:
--- a/drivers/accessibility/speakup/speakup.h
+++ b/drivers/accessibility/speakup/speakup.h
@@ -70,7 +70,6 @@ void spk_do_flush(void);
void speakup_start_ttys(void);
void synth_buffer_add(u16 ch);
void synth_buffer_clear(void);
-void speakup_clear_selection(void);
int speakup_set_selection(struct tty_struct *tty);
void speakup_cancel_selection(void);
int speakup_paste_selection(struct tty_struct *tty);