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authorJiri Slaby <jslaby@suse.cz>2019-04-17 11:58:53 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-04-25 12:37:41 +0300
commit4cdd17ba1dff20ffc99fdbd2e6f0201fc7fe67df (patch)
tree359743ba104e7ae321faa8caa36a745d56293533 /drivers/tty
parent6bc3703dcf0e6891a55987cbae0823c8c185c5e5 (diff)
downloadlinux-4cdd17ba1dff20ffc99fdbd2e6f0201fc7fe67df.tar.xz
TTY: serial_core, add ->install
We need to compute the uart state only on the first open. This is usually what is done in the ->install hook. serial_core used to do this in ->open on every open. So move it to ->install. As a side effect, it ensures the state is set properly in the window after tty_init_dev is called, but before uart_open. This fixes a bunch of races between tty_open and flush_to_ldisc we were dealing with recently. One of such bugs was attempted to fix in commit fedb5760648a (serial: fix race between flush_to_ldisc and tty_open), but it only took care of a couple of functions (uart_start and uart_unthrottle). I was able to reproduce the crash on a SLE system, but in uart_write_room which is also called from flush_to_ldisc via process_echoes. I was *unable* to reproduce the bug locally. It is due to having this patch in my queue since 2012! general protection fault: 0000 [#1] SMP KASAN PTI CPU: 1 PID: 5 Comm: kworker/u4:0 Tainted: G L 4.12.14-396-default #1 SLE15-SP1 (unreleased) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-0-ga698c89-prebuilt.qemu.org 04/01/2014 Workqueue: events_unbound flush_to_ldisc task: ffff8800427d8040 task.stack: ffff8800427f0000 RIP: 0010:uart_write_room+0xc4/0x590 RSP: 0018:ffff8800427f7088 EFLAGS: 00010202 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 000000000000002f RSI: 00000000000000ee RDI: ffff88003888bd90 RBP: ffffffffb9545850 R08: 0000000000000001 R09: 0000000000000400 R10: ffff8800427d825c R11: 000000000000006e R12: 1ffff100084fee12 R13: ffffc900004c5000 R14: ffff88003888bb28 R15: 0000000000000178 FS: 0000000000000000(0000) GS:ffff880043300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000561da0794148 CR3: 000000000ebf4000 CR4: 00000000000006e0 Call Trace: tty_write_room+0x6d/0xc0 __process_echoes+0x55/0x870 n_tty_receive_buf_common+0x105e/0x26d0 tty_ldisc_receive_buf+0xb7/0x1c0 tty_port_default_receive_buf+0x107/0x180 flush_to_ldisc+0x35d/0x5c0 ... 0 in rbx means tty->driver_data is NULL in uart_write_room. 0x178 is tried to be dereferenced (0x178 >> 3 is 0x2f in rdx) at uart_write_room+0xc4. 0x178 is exactly (struct uart_state *)NULL->refcount used in uart_port_lock from uart_write_room. So revert the upstream commit here as my local patch should fix the whole family. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Cc: Li RongQing <lirongqing@baidu.com> Cc: Wang Li <wangli39@baidu.com> Cc: Zhang Yu <zhangyu31@baidu.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: stable <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/serial/serial_core.c24
1 files changed, 13 insertions, 11 deletions
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 69f48717546b..0decb0bf991d 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -130,9 +130,6 @@ static void uart_start(struct tty_struct *tty)
struct uart_port *port;
unsigned long flags;
- if (!state)
- return;
-
port = uart_port_lock(state, flags);
__uart_start(tty);
uart_port_unlock(port, flags);
@@ -730,9 +727,6 @@ static void uart_unthrottle(struct tty_struct *tty)
upstat_t mask = UPSTAT_SYNC_FIFO;
struct uart_port *port;
- if (!state)
- return;
-
port = uart_port_ref(state);
if (!port)
return;
@@ -1747,6 +1741,16 @@ static void uart_dtr_rts(struct tty_port *port, int raise)
uart_port_deref(uport);
}
+static int uart_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+ struct uart_driver *drv = driver->driver_state;
+ struct uart_state *state = drv->state + tty->index;
+
+ tty->driver_data = state;
+
+ return tty_standard_install(driver, tty);
+}
+
/*
* Calls to uart_open are serialised by the tty_lock in
* drivers/tty/tty_io.c:tty_open()
@@ -1759,11 +1763,8 @@ static void uart_dtr_rts(struct tty_port *port, int raise)
*/
static int uart_open(struct tty_struct *tty, struct file *filp)
{
- struct uart_driver *drv = tty->driver->driver_state;
- int retval, line = tty->index;
- struct uart_state *state = drv->state + line;
-
- tty->driver_data = state;
+ struct uart_state *state = tty->driver_data;
+ int retval;
retval = tty_port_open(&state->port, tty, filp);
if (retval > 0)
@@ -2448,6 +2449,7 @@ static void uart_poll_put_char(struct tty_driver *driver, int line, char ch)
#endif
static const struct tty_operations uart_ops = {
+ .install = uart_install,
.open = uart_open,
.close = uart_close,
.write = uart_write,