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tty: n_gsm: avoid call of sleeping functions from atomic context
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Syzkaller reports the following problem:

BUG: sleeping function called from invalid context at kernel/printk/printk.c:2347
in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1105, name: syz-executor423
3 locks held by syz-executor423/1105:
 #0: ffff8881468b9098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x90 drivers/tty/tty_ldisc.c:266
 STMicroelectronics#1: ffff8881468b9130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: tty_write_lock drivers/tty/tty_io.c:952 [inline]
 STMicroelectronics#1: ffff8881468b9130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: do_tty_write drivers/tty/tty_io.c:975 [inline]
 STMicroelectronics#1: ffff8881468b9130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: file_tty_write.constprop.0+0x2a8/0x8e0 drivers/tty/tty_io.c:1118
 STMicroelectronics#2: ffff88801b06c398 (&gsm->tx_lock){....}-{2:2}, at: gsmld_write+0x5e/0x150 drivers/tty/n_gsm.c:2717
irq event stamp: 3482
hardirqs last  enabled at (3481): [<ffffffff81d13343>] __get_reqs_available+0x143/0x2f0 fs/aio.c:946
hardirqs last disabled at (3482): [<ffffffff87d39722>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (3482): [<ffffffff87d39722>] _raw_spin_lock_irqsave+0x52/0x60 kernel/locking/spinlock.c:159
softirqs last  enabled at (3408): [<ffffffff87e01002>] asm_call_irq_on_stack+0x12/0x20
softirqs last disabled at (3401): [<ffffffff87e01002>] asm_call_irq_on_stack+0x12/0x20
Preemption disabled at:
[<0000000000000000>] 0x0
CPU: 2 PID: 1105 Comm: syz-executor423 Not tainted 5.10.137-syzkaller #0
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x107/0x167 lib/dump_stack.c:118
 ___might_sleep.cold+0x1e8/0x22e kernel/sched/core.c:7304
 console_lock+0x19/0x80 kernel/printk/printk.c:2347
 do_con_write+0x113/0x1de0 drivers/tty/vt/vt.c:2909
 con_write+0x22/0xc0 drivers/tty/vt/vt.c:3296
 gsmld_write+0xd0/0x150 drivers/tty/n_gsm.c:2720
 do_tty_write drivers/tty/tty_io.c:1028 [inline]
 file_tty_write.constprop.0+0x502/0x8e0 drivers/tty/tty_io.c:1118
 call_write_iter include/linux/fs.h:1903 [inline]
 aio_write+0x355/0x7b0 fs/aio.c:1580
 __io_submit_one fs/aio.c:1952 [inline]
 io_submit_one+0xf45/0x1a90 fs/aio.c:1999
 __do_sys_io_submit fs/aio.c:2058 [inline]
 __se_sys_io_submit fs/aio.c:2028 [inline]
 __x64_sys_io_submit+0x18c/0x2f0 fs/aio.c:2028
 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xc6

The problem happens in the following control flow:

gsmld_write(...)
spin_lock_irqsave(&gsm->tx_lock, flags) // taken a spinlock on TX data
 con_write(...)
  do_con_write(...)
   console_lock()
    might_sleep() // -> bug

As far as console_lock() might sleep it should not be called with
spinlock held.

The patch replaces tx_lock spinlock with mutex in order to avoid the
problem.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 32dd59f ("tty: n_gsm: fix race condition in gsmld_write()")
Cc: stable <stable@kernel.org>
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Link: https://lore.kernel.org/r/20220829131640.69254-3-pchelkin@ispras.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@gregkh
Fedor Pchelkin authored and gregkh committed Aug 30, 2022
1 parent c9ab053 commit 902e02e
Showing 1 changed file with 24 additions and 29 deletions.
53 changes: 24 additions & 29 deletions drivers/tty/n_gsm.c
View file
Expand Up @@ -248,7 +248,7 @@ struct gsm_mux {
bool constipated; /* Asked by remote to shut up */
bool has_devices; /* Devices were registered */

spinlock_t tx_lock;
struct mutex tx_mutex;
unsigned int tx_bytes; /* TX data outstanding */
#define TX_THRESH_HI 8192
#define TX_THRESH_LO 2048
Expand Down Expand Up @@ -680,7 +680,6 @@ static int gsm_send(struct gsm_mux *gsm, int addr, int cr, int control)
struct gsm_msg *msg;
u8 *dp;
int ocr;
unsigned long flags;

msg = gsm_data_alloc(gsm, addr, 0, control);
if (!msg)
Expand All @@ -702,10 +701,10 @@ static int gsm_send(struct gsm_mux *gsm, int addr, int cr, int control)

gsm_print_packet("Q->", addr, cr, control, NULL, 0);

spin_lock_irqsave(&gsm->tx_lock, flags);
mutex_lock(&gsm->tx_mutex);
list_add_tail(&msg->list, &gsm->tx_ctrl_list);
gsm->tx_bytes += msg->len;
spin_unlock_irqrestore(&gsm->tx_lock, flags);
mutex_unlock(&gsm->tx_mutex);
gsmld_write_trigger(gsm);

return 0;
Expand All @@ -730,15 +729,15 @@ static void gsm_dlci_clear_queues(struct gsm_mux *gsm, struct gsm_dlci *dlci)
spin_unlock_irqrestore(&dlci->lock, flags);

/* Clear data packets in MUX write queue */
spin_lock_irqsave(&gsm->tx_lock, flags);
mutex_lock(&gsm->tx_mutex);
list_for_each_entry_safe(msg, nmsg, &gsm->tx_data_list, list) {
if (msg->addr != addr)
continue;
gsm->tx_bytes -= msg->len;
list_del(&msg->list);
kfree(msg);
}
spin_unlock_irqrestore(&gsm->tx_lock, flags);
mutex_unlock(&gsm->tx_mutex);
}

/**
Expand Down Expand Up @@ -1024,10 +1023,9 @@ static void __gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)

static void gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
{
unsigned long flags;
spin_lock_irqsave(&dlci->gsm->tx_lock, flags);
mutex_lock(&dlci->gsm->tx_mutex);
__gsm_data_queue(dlci, msg);
spin_unlock_irqrestore(&dlci->gsm->tx_lock, flags);
mutex_unlock(&dlci->gsm->tx_mutex);
}

/**
Expand All @@ -1039,7 +1037,7 @@ static void gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
* is data. Keep to the MRU of the mux. This path handles the usual tty
* interface which is a byte stream with optional modem data.
*
* Caller must hold the tx_lock of the mux.
* Caller must hold the tx_mutex of the mux.
*/

static int gsm_dlci_data_output(struct gsm_mux *gsm, struct gsm_dlci *dlci)
Expand Down Expand Up @@ -1099,7 +1097,7 @@ static int gsm_dlci_data_output(struct gsm_mux *gsm, struct gsm_dlci *dlci)
* is data. Keep to the MRU of the mux. This path handles framed data
* queued as skbuffs to the DLCI.
*
* Caller must hold the tx_lock of the mux.
* Caller must hold the tx_mutex of the mux.
*/

static int gsm_dlci_data_output_framed(struct gsm_mux *gsm,
Expand All @@ -1115,7 +1113,7 @@ static int gsm_dlci_data_output_framed(struct gsm_mux *gsm,
if (dlci->adaption == 4)
overhead = 1;

/* dlci->skb is locked by tx_lock */
/* dlci->skb is locked by tx_mutex */
if (dlci->skb == NULL) {
dlci->skb = skb_dequeue_tail(&dlci->skb_list);
if (dlci->skb == NULL)
Expand Down Expand Up @@ -1169,7 +1167,7 @@ static int gsm_dlci_data_output_framed(struct gsm_mux *gsm,
* Push an empty frame in to the transmit queue to update the modem status
* bits and to transmit an optional break.
*
* Caller must hold the tx_lock of the mux.
* Caller must hold the tx_mutex of the mux.
*/

static int gsm_dlci_modem_output(struct gsm_mux *gsm, struct gsm_dlci *dlci,
Expand Down Expand Up @@ -1283,13 +1281,12 @@ static int gsm_dlci_data_sweep(struct gsm_mux *gsm)

static void gsm_dlci_data_kick(struct gsm_dlci *dlci)
{
unsigned long flags;
int sweep;

if (dlci->constipated)
return;

spin_lock_irqsave(&dlci->gsm->tx_lock, flags);
mutex_lock(&dlci->gsm->tx_mutex);
/* If we have nothing running then we need to fire up */
sweep = (dlci->gsm->tx_bytes < TX_THRESH_LO);
if (dlci->gsm->tx_bytes == 0) {
Expand All @@ -1300,7 +1297,7 @@ static void gsm_dlci_data_kick(struct gsm_dlci *dlci)
}
if (sweep)
gsm_dlci_data_sweep(dlci->gsm);
spin_unlock_irqrestore(&dlci->gsm->tx_lock, flags);
mutex_unlock(&dlci->gsm->tx_mutex);
}

/*
Expand Down Expand Up @@ -1994,14 +1991,13 @@ static void gsm_dlci_command(struct gsm_dlci *dlci, const u8 *data, int len)
static void gsm_kick_timeout(struct work_struct *work)
{
struct gsm_mux *gsm = container_of(work, struct gsm_mux, kick_timeout.work);
unsigned long flags;
int sent = 0;

spin_lock_irqsave(&gsm->tx_lock, flags);
mutex_lock(&gsm->tx_mutex);
/* If we have nothing running then we need to fire up */
if (gsm->tx_bytes < TX_THRESH_LO)
sent = gsm_dlci_data_sweep(gsm);
spin_unlock_irqrestore(&gsm->tx_lock, flags);
mutex_unlock(&gsm->tx_mutex);

if (sent && debug & 4)
pr_info("%s TX queue stalled\n", __func__);
Expand Down Expand Up @@ -2531,6 +2527,7 @@ static void gsm_free_mux(struct gsm_mux *gsm)
break;
}
}
mutex_destroy(&gsm->tx_mutex);
mutex_destroy(&gsm->mutex);
kfree(gsm->txframe);
kfree(gsm->buf);
Expand Down Expand Up @@ -2602,6 +2599,7 @@ static struct gsm_mux *gsm_alloc_mux(void)
}
spin_lock_init(&gsm->lock);
mutex_init(&gsm->mutex);
mutex_init(&gsm->tx_mutex);
kref_init(&gsm->ref);
INIT_LIST_HEAD(&gsm->tx_ctrl_list);
INIT_LIST_HEAD(&gsm->tx_data_list);
Expand All @@ -2610,7 +2608,6 @@ static struct gsm_mux *gsm_alloc_mux(void)
INIT_WORK(&gsm->tx_work, gsmld_write_task);
init_waitqueue_head(&gsm->event);
spin_lock_init(&gsm->control_lock);
spin_lock_init(&gsm->tx_lock);

gsm->t1 = T1;
gsm->t2 = T2;
Expand All @@ -2635,6 +2632,7 @@ static struct gsm_mux *gsm_alloc_mux(void)
}
spin_unlock(&gsm_mux_lock);
if (i == MAX_MUX) {
mutex_destroy(&gsm->tx_mutex);
mutex_destroy(&gsm->mutex);
kfree(gsm->txframe);
kfree(gsm->buf);
Expand Down Expand Up @@ -2790,17 +2788,16 @@ static void gsmld_write_trigger(struct gsm_mux *gsm)
static void gsmld_write_task(struct work_struct *work)
{
struct gsm_mux *gsm = container_of(work, struct gsm_mux, tx_work);
unsigned long flags;
int i, ret;

/* All outstanding control channel and control messages and one data
* frame is sent.
*/
ret = -ENODEV;
spin_lock_irqsave(&gsm->tx_lock, flags);
mutex_lock(&gsm->tx_mutex);
if (gsm->tty)
ret = gsm_data_kick(gsm);
spin_unlock_irqrestore(&gsm->tx_lock, flags);
mutex_unlock(&gsm->tx_mutex);

if (ret >= 0)
for (i = 0; i < NUM_DLCI; i++)
Expand Down Expand Up @@ -3008,21 +3005,20 @@ static ssize_t gsmld_write(struct tty_struct *tty, struct file *file,
const unsigned char *buf, size_t nr)
{
struct gsm_mux *gsm = tty->disc_data;
unsigned long flags;
int space;
int ret;

if (!gsm)
return -ENODEV;

ret = -ENOBUFS;
spin_lock_irqsave(&gsm->tx_lock, flags);
mutex_lock(&gsm->tx_mutex);
space = tty_write_room(tty);
if (space >= nr)
ret = tty->ops->write(tty, buf, nr);
else
set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
spin_unlock_irqrestore(&gsm->tx_lock, flags);
mutex_unlock(&gsm->tx_mutex);

return ret;
}
Expand Down Expand Up @@ -3319,14 +3315,13 @@ static struct tty_ldisc_ops tty_ldisc_packet = {
static void gsm_modem_upd_via_data(struct gsm_dlci *dlci, u8 brk)
{
struct gsm_mux *gsm = dlci->gsm;
unsigned long flags;

if (dlci->state != DLCI_OPEN || dlci->adaption != 2)
return;

spin_lock_irqsave(&gsm->tx_lock, flags);
mutex_lock(&gsm->tx_mutex);
gsm_dlci_modem_output(gsm, dlci, brk);
spin_unlock_irqrestore(&gsm->tx_lock, flags);
mutex_unlock(&gsm->tx_mutex);
}

/**
Expand Down

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