[Bluetooth] Fix L2CAP and HCI setsockopt() information leaks

The L2CAP and HCI setsockopt() implementations have a small information
leak that makes it possible to leak kernel stack memory to userspace.

If the optlen parameter is 0, no data will be copied by copy_from_user(),
but the uninitialized stack buffer will be read and stored later. A call
to getsockopt() can now retrieve the leaked information.

To fix this problem the stack buffer given to copy_from_user() must be
initialized with the current settings.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index a5867879b615..a59b1fb63b76 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -954,11 +954,17 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname, ch
 
         switch (optname) {
         case L2CAP_OPTIONS:
+                opts.imtu     = l2cap_pi(sk)->imtu;
+                opts.omtu     = l2cap_pi(sk)->omtu;
+                opts.flush_to = l2cap_pi(sk)->flush_to;
+                opts.mode     = 0x00;
+
                 len = min_t(unsigned int, sizeof(opts), optlen);
                 if (copy_from_user((char *) &opts, optval, len)) {
                         err = -EFAULT;
                         break;
                 }
+
                 l2cap_pi(sk)->imtu  = opts.imtu;
                 l2cap_pi(sk)->omtu  = opts.omtu;
                 break;