tty: n_gsm: require CAP_NET_ADMIN to attach N_GSM0710 ldisc

commit 67c37756898a5a6b2941a13ae7260c89b54e0d88 upstream.

Any unprivileged user can attach N_GSM0710 ldisc, but it requires
CAP_NET_ADMIN to create a GSM network anyway.

Require initial namespace CAP_NET_ADMIN to do that.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Link: https://lore.kernel.org/r/20230731185942.279611-1-cascardo@canonical.com
Cc: Salvatore Bonaccorso <carnil@debian.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 2337402f95df7904f79beb04bcdec89ddbdbaecc..4ff3010a82eaa5ceeeceb31c86225d0f5edbc043 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2827,6 +2827,9 @@ static int gsmld_open(struct tty_struct *tty)
 {
        struct gsm_mux *gsm;
 
+       if (!capable(CAP_NET_ADMIN))
+               return -EPERM;
+
        if (tty->ops->write == NULL)
                return -EINVAL;