The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Possible dependencies:

902e02ea9385 ("tty: n_gsm: avoid call of sleeping functions from atomic context") c9ab053e56ce ("tty: n_gsm: replace kicktimer with delayed_work") 4bb1a53be85f ("tty: n_gsm: initialize more members at gsm_alloc_mux()") 734966043860 ("tty: n_gsm: fix resource allocation order in gsm_activate_mux()") 0af021678d5d ("tty: n_gsm: fix deadlock and link starvation in outgoing data path") 32dd59f96924 ("tty: n_gsm: fix race condition in gsmld_write()") bec0224816d1 ("tty: n_gsm: fix non flow control frames during mux flow off") c568f7086c6e ("tty: n_gsm: fix missing timer to handle stalled links") 556fc8ac0651 ("tty: n_gsm: fix wrong queuing behavior in gsm_dlci_data_output()") 01aecd917114 ("tty: n_gsm: fix tty registration before control channel open") 925ea0fa5277 ("tty: n_gsm: Fix packet data hex dump output") f4f7d6328721 ("tty: n_gsm: fix software flow control handling") c19ffe00fed6 ("tty: n_gsm: fix invalid use of MSC in advanced option") a8c5b8255f8a ("tty: n_gsm: fix broken virtual tty handling") 48473802506d ("tty: n_gsm: fix missing update of modem controls after DLCI open") 73029a4d7161 ("tty: n_gsm: fix reset fifo race condition") 398867f59f95 ("tty: n_gsm: fix wrong command frame length field encoding") 17eac6520285 ("tty: n_gsm: fix missing explicit ldisc flush") deefc58bafb4 ("tty: n_gsm: fix wrong DLCI release order") 7a0e4b1733b6 ("tty: n_gsm: fix frame reception handling")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 902e02ea9385373ce4b142576eef41c642703955 Mon Sep 17 00:00:00 2001 From: Fedor Pchelkin pchelkin@ispras.ru Date: Mon, 29 Aug 2022 16:16:40 +0300 Subject: [PATCH] tty: n_gsm: avoid call of sleeping functions from atomic context

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 #1: ffff8881468b9130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: tty_write_lock drivers/tty/tty_io.c:952 [inline] #1: ffff8881468b9130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: do_tty_write drivers/tty/tty_io.c:975 [inline] #1: ffff8881468b9130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: file_tty_write.constprop.0+0x2a8/0x8e0 drivers/tty/tty_io.c:1118 #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: 32dd59f96924 ("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

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index e23225aff5d9..01c112e2e214 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -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 @@ -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) @@ -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; @@ -730,7 +729,7 @@ 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; @@ -738,7 +737,7 @@ static void gsm_dlci_clear_queues(struct gsm_mux *gsm, struct gsm_dlci *dlci) list_del(&msg->list); kfree(msg); } - spin_unlock_irqrestore(&gsm->tx_lock, flags); + mutex_unlock(&gsm->tx_mutex); }

/** @@ -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); }

/** @@ -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) @@ -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, @@ -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) @@ -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, @@ -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) { @@ -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); }

/* @@ -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__); @@ -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); @@ -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); @@ -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; @@ -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); @@ -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++) @@ -3008,7 +3005,6 @@ 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;

@@ -3016,13 +3012,13 @@ static ssize_t gsmld_write(struct tty_struct *tty, struct file *file, 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; } @@ -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); }

/**