Bluetooth: Properly check L2CAP config option output buffer length

Bluetooth: Properly check L2CAP config option output buffer length

commit e860d2c904d1a9f38a24eb44c9f34b8f915a6ea3 upstream.

Validate the output buffer length for L2CAP config requests and responses
to avoid overflowing the stack buffer used for building the option blocks.

Signed-off-by: Ben Seri <ben@armis.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[sw0312.kim: Cherry-pick from linux-4.9.y tree to fix CVE-2017-1000251]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I6685f0bfbc098bbb284342453295da04cb19e29c