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Subject[PATCH] tty: ttynull: implement console write
Date
Since commit 3579b59c7edc475013ae769a2d26d99733c95f13 ("printk: refactor
and rework printing logic"), con->write is called without checking if it
is implemented in the console driver. This does make some sense, because
for all "normal" consoles it is vital to have a write function.
As the ttynull console driver does not need any console output the write
function was not implemented. This caused a "unable to handle kernel NULL
pointer dereference" when the write function is called now.

To fix this issue, implement an empty write function.

Signed-off-by: Michael Thalmeier <michael.thalmeier@hale.at>
Cc: stable@vger.kernel.org
---
drivers/tty/ttynull.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c
index 1d4438472442..6e9323544a7d 100644
--- a/drivers/tty/ttynull.c
+++ b/drivers/tty/ttynull.c
@@ -40,6 +40,12 @@ static unsigned int ttynull_write_room(struct tty_struct *tty)
return 65536;
}

+
+static void ttynull_console_write(struct console *co, const char *buf,
+ unsigned count)
+{
+}
+
static const struct tty_operations ttynull_ops = {
.open = ttynull_open,
.close = ttynull_close,
@@ -56,6 +62,7 @@ static struct tty_driver *ttynull_device(struct console *c, int *index)

static struct console ttynull_console = {
.name = "ttynull",
+ .write = ttynull_console_write,
.device = ttynull_device,
};

--
2.39.1
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