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tty: n_gsm: avoid call of sleeping functions from atomic context
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commit 902e02e upstream.

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 Sep 15, 2022
1 parent fb6cadd commit eb75efd
Showing 1 changed file with 18 additions and 21 deletions.
39 changes: 18 additions & 21 deletions drivers/tty/n_gsm.c
View file
Expand Up @@ -235,7 +235,7 @@ struct gsm_mux {
int old_c_iflag; /* termios c_iflag value before attach */
bool constipated; /* Asked by remote to shut up */

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 @@ -820,15 +820,14 @@ static void __gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
*
* Add data to the transmit queue and try and get stuff moving
* out of the mux tty if not already doing so. Take the
* the gsm tx lock and dlci lock.
* the gsm tx mutex and dlci lock.
*/

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 @@ -840,7 +839,7 @@ 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 @@ -903,7 +902,7 @@ 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 @@ -919,7 +918,7 @@ 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 @@ -1019,13 +1018,12 @@ static void 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 @@ -1036,7 +1034,7 @@ 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 @@ -1258,7 +1256,6 @@ static void gsm_control_message(struct gsm_mux *gsm, unsigned int command,
const u8 *data, int clen)
{
u8 buf[1];
unsigned long flags;

switch (command) {
case CMD_CLD: {
Expand All @@ -1280,9 +1277,9 @@ static void gsm_control_message(struct gsm_mux *gsm, unsigned int command,
gsm->constipated = false;
gsm_control_reply(gsm, CMD_FCON, NULL, 0);
/* Kick the link in case it is idling */
spin_lock_irqsave(&gsm->tx_lock, flags);
mutex_lock(&gsm->tx_mutex);
gsm_data_kick(gsm, NULL);
spin_unlock_irqrestore(&gsm->tx_lock, flags);
mutex_unlock(&gsm->tx_mutex);
break;
case CMD_FCOFF:
/* Modem wants us to STFU */
Expand Down Expand Up @@ -2228,6 +2225,7 @@ 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 @@ -2299,12 +2297,12 @@ 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_list);
timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0);
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 @@ -2329,6 +2327,7 @@ 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 @@ -2653,16 +2652,15 @@ static int gsmld_open(struct tty_struct *tty)
static void gsmld_write_wakeup(struct tty_struct *tty)
{
struct gsm_mux *gsm = tty->disc_data;
unsigned long flags;

/* Queue poll */
clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
spin_lock_irqsave(&gsm->tx_lock, flags);
mutex_lock(&gsm->tx_mutex);
gsm_data_kick(gsm, NULL);
if (gsm->tx_bytes < TX_THRESH_LO) {
gsm_dlci_data_sweep(gsm);
}
spin_unlock_irqrestore(&gsm->tx_lock, flags);
mutex_unlock(&gsm->tx_mutex);
}

/**
Expand Down Expand Up @@ -2705,21 +2703,20 @@ 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

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