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Subject[PATCH] tty: fix data race in n_tty_receive_buf_common
Date
There can be a race, if receive_buf call comes before
tty initialization completes in n_tty_open and tty->disc_data
may be NULL.

CPU0 cpu1
---- ----
000|n_tty_receive_buf_common() n_tty_open()
-001|n_tty_receive_buf2() tty_ldisc_open.isra.3()
-002|tty_ldisc_receive_buf(inline) tty_ldisc_setup()

If tty->disc_data is NULL, then return from flush_to_ldisc

Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org>

diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 25d7368..5d49183 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -35,6 +35,9 @@ static int tty_port_default_receive_buf(struct tty_port *port,
if (!disc)
return 0;

+ if (!tty->disc_data)
+ return 0;
+
ret = tty_ldisc_receive_buf(disc, p, (char *)f, count);

tty_ldisc_deref(disc);
--
1.9.1
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