[added,to,the,v4.1,stable,tree] tty: fix __tty_insert_flip_char regression

Message ID 20171006111704.25872-100-alexander.levin@verizon.com
State New
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Series
  • [added,to,the,v4.1,stable,tree] tty: fix __tty_insert_flip_char regression
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Commit Message

Levin, Alexander (Sasha Levin) Oct. 6, 2017, 11:17 a.m.
From: Arnd Bergmann <arnd@arndb.de>


This patch has been added to the v4.1 stable tree. If you have any
objections, please let us know.

-- 
2.11.0

Patch

===============

[ Upstream commit 8a5a90a2a477b86a3dc2eaa5a706db9bfdd647ca ]

Sergey noticed a small but fatal mistake in __tty_insert_flip_char,
leading to an oops in an interrupt handler when using any serial
port.

The problem is that I accidentally took the tty_buffer pointer
before calling __tty_buffer_request_room(), which replaces the
buffer. This moves the pointer lookup to the right place after
allocating the new buffer space.

Fixes: 979990c62848 ("tty: improve tty_insert_flip_char() fast path")
Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
---
 drivers/tty/tty_buffer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 1e485adf008a..25c15910af77 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -366,12 +366,13 @@  EXPORT_SYMBOL(tty_insert_flip_string_flags);
  */
 int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
 {
-	struct tty_buffer *tb = port->buf.tail;
+	struct tty_buffer *tb;
 	int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
 
 	if (!__tty_buffer_request_room(port, 1, flags))
 		return 0;
 
+	tb = port->buf.tail;
 	if (~tb->flags & TTYB_NORMAL)
 		*flag_buf_ptr(tb, tb->used) = flag;
 	*char_buf_ptr(tb, tb->used++) = ch;