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Subject[PATCH 1/5] Bluetooth: Add RFCOMM TTY write return error codes
It appears that rfcomm_tty_write() does not check that the
passed in TTY device_data is not NULL and also does not check
that the RFCOMM DLC serial data link pointer is not NULL.

A kernel crash was observed whilst SLIP was bound to /dev/rfcomm0
but the /dev/rfcomm0 had subsequently disconnected. Unfortunately,
SLIP attempted to write to the now non-existant RFCOMM TTY device
which caused a NULL pointer dereference because the device_data
no longer existed.

Therefore, add NULL pointer checks for the dev and dlc pointers
and output kernel error debug to show that NULL had been detected.

Signed-off-by: Dean Jenkins <>
net/bluetooth/rfcomm/tty.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index b6e44ad..56d28d1 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -761,12 +761,24 @@ static void rfcomm_tty_close(struct tty_struct *tty, struct file *filp)
static int rfcomm_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
struct rfcomm_dev *dev = (struct rfcomm_dev *) tty->driver_data;
- struct rfcomm_dlc *dlc = dev->dlc;
+ struct rfcomm_dlc *dlc;
struct sk_buff *skb;
int err = 0, sent = 0, size;

BT_DBG("tty %p count %d", tty, count);

+ if (!dev) {
+ BT_ERR("RFCOMM TTY device data structure does not exist");
+ return -ENODEV;
+ }
+ dlc = dev->dlc;
+ if (!dlc) {
+ BT_ERR("RFCOMM serial data link does not exist");
+ return -ENOLINK;
+ }
while (count) {
size = min_t(uint, count, dlc->mtu);


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