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1 | From 4cdd17ba1dff20ffc99fdbd2e6f0201fc7fe67df Mon Sep 17 00:00:00 2001 | |
2 | From: Jiri Slaby <jslaby@suse.cz> | |
3 | Date: Wed, 17 Apr 2019 10:58:53 +0200 | |
4 | Subject: TTY: serial_core, add ->install | |
5 | ||
6 | From: Jiri Slaby <jslaby@suse.cz> | |
7 | ||
8 | commit 4cdd17ba1dff20ffc99fdbd2e6f0201fc7fe67df upstream. | |
9 | ||
10 | We need to compute the uart state only on the first open. This is | |
11 | usually what is done in the ->install hook. serial_core used to do this | |
12 | in ->open on every open. So move it to ->install. | |
13 | ||
14 | As a side effect, it ensures the state is set properly in the window | |
15 | after tty_init_dev is called, but before uart_open. This fixes a bunch | |
16 | of races between tty_open and flush_to_ldisc we were dealing with | |
17 | recently. | |
18 | ||
19 | One of such bugs was attempted to fix in commit fedb5760648a (serial: | |
20 | fix race between flush_to_ldisc and tty_open), but it only took care of | |
21 | a couple of functions (uart_start and uart_unthrottle). I was able to | |
22 | reproduce the crash on a SLE system, but in uart_write_room which is | |
23 | also called from flush_to_ldisc via process_echoes. I was *unable* to | |
24 | reproduce the bug locally. It is due to having this patch in my queue | |
25 | since 2012! | |
26 | ||
27 | general protection fault: 0000 [#1] SMP KASAN PTI | |
28 | CPU: 1 PID: 5 Comm: kworker/u4:0 Tainted: G L 4.12.14-396-default #1 SLE15-SP1 (unreleased) | |
29 | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-0-ga698c89-prebuilt.qemu.org 04/01/2014 | |
30 | Workqueue: events_unbound flush_to_ldisc | |
31 | task: ffff8800427d8040 task.stack: ffff8800427f0000 | |
32 | RIP: 0010:uart_write_room+0xc4/0x590 | |
33 | RSP: 0018:ffff8800427f7088 EFLAGS: 00010202 | |
34 | RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 | |
35 | RDX: 000000000000002f RSI: 00000000000000ee RDI: ffff88003888bd90 | |
36 | RBP: ffffffffb9545850 R08: 0000000000000001 R09: 0000000000000400 | |
37 | R10: ffff8800427d825c R11: 000000000000006e R12: 1ffff100084fee12 | |
38 | R13: ffffc900004c5000 R14: ffff88003888bb28 R15: 0000000000000178 | |
39 | FS: 0000000000000000(0000) GS:ffff880043300000(0000) knlGS:0000000000000000 | |
40 | CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 | |
41 | CR2: 0000561da0794148 CR3: 000000000ebf4000 CR4: 00000000000006e0 | |
42 | Call Trace: | |
43 | tty_write_room+0x6d/0xc0 | |
44 | __process_echoes+0x55/0x870 | |
45 | n_tty_receive_buf_common+0x105e/0x26d0 | |
46 | tty_ldisc_receive_buf+0xb7/0x1c0 | |
47 | tty_port_default_receive_buf+0x107/0x180 | |
48 | flush_to_ldisc+0x35d/0x5c0 | |
49 | ... | |
50 | ||
51 | 0 in rbx means tty->driver_data is NULL in uart_write_room. 0x178 is | |
52 | tried to be dereferenced (0x178 >> 3 is 0x2f in rdx) at | |
53 | uart_write_room+0xc4. 0x178 is exactly (struct uart_state *)NULL->refcount | |
54 | used in uart_port_lock from uart_write_room. | |
55 | ||
56 | So revert the upstream commit here as my local patch should fix the | |
57 | whole family. | |
58 | ||
59 | Signed-off-by: Jiri Slaby <jslaby@suse.cz> | |
60 | Cc: Li RongQing <lirongqing@baidu.com> | |
61 | Cc: Wang Li <wangli39@baidu.com> | |
62 | Cc: Zhang Yu <zhangyu31@baidu.com> | |
63 | Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> | |
64 | Cc: stable <stable@vger.kernel.org> | |
65 | Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> | |
66 | ||
67 | --- | |
68 | drivers/tty/serial/serial_core.c | 24 +++++++++++++----------- | |
69 | 1 file changed, 13 insertions(+), 11 deletions(-) | |
70 | ||
71 | --- a/drivers/tty/serial/serial_core.c | |
72 | +++ b/drivers/tty/serial/serial_core.c | |
73 | @@ -141,9 +141,6 @@ static void uart_start(struct tty_struct | |
74 | struct uart_port *port; | |
75 | unsigned long flags; | |
76 | ||
77 | - if (!state) | |
78 | - return; | |
79 | - | |
80 | port = uart_port_lock(state, flags); | |
81 | __uart_start(tty); | |
82 | uart_port_unlock(port, flags); | |
83 | @@ -1714,11 +1711,8 @@ static void uart_dtr_rts(struct tty_port | |
84 | */ | |
85 | static int uart_open(struct tty_struct *tty, struct file *filp) | |
86 | { | |
87 | - struct uart_driver *drv = tty->driver->driver_state; | |
88 | - int retval, line = tty->index; | |
89 | - struct uart_state *state = drv->state + line; | |
90 | - | |
91 | - tty->driver_data = state; | |
92 | + struct uart_state *state = tty->driver_data; | |
93 | + int retval; | |
94 | ||
95 | retval = tty_port_open(&state->port, tty, filp); | |
96 | if (retval > 0) | |
97 | @@ -2409,9 +2403,6 @@ static void uart_poll_put_char(struct tt | |
98 | struct uart_state *state = drv->state + line; | |
99 | struct uart_port *port; | |
100 | ||
101 | - if (!state) | |
102 | - return; | |
103 | - | |
104 | port = uart_port_ref(state); | |
105 | if (!port) | |
106 | return; | |
107 | @@ -2423,7 +2414,18 @@ static void uart_poll_put_char(struct tt | |
108 | } | |
109 | #endif | |
110 | ||
111 | +static int uart_install(struct tty_driver *driver, struct tty_struct *tty) | |
112 | +{ | |
113 | + struct uart_driver *drv = driver->driver_state; | |
114 | + struct uart_state *state = drv->state + tty->index; | |
115 | + | |
116 | + tty->driver_data = state; | |
117 | + | |
118 | + return tty_standard_install(driver, tty); | |
119 | +} | |
120 | + | |
121 | static const struct tty_operations uart_ops = { | |
122 | + .install = uart_install, | |
123 | .open = uart_open, | |
124 | .close = uart_close, | |
125 | .write = uart_write, |