[PATCH] pps: require CAP_SYS_TIME to attach N_PPS ldisc

[Hungyu Lin <dennylin0707@gmail.com>]

Any unprivileged user can attach the N_PPS ldisc to a pty, and every
attach registers a PPS source. At most PPS_MAX_SOURCES (256) sources can
exist, so such a user can take all of them, after which registering a
real PPS source fails with -EBUSY.

Require CAP_SYS_TIME to attach N_PPS, the capability that PPS_SETPARAMS
already needs to configure a source.

Fixes: a0880df0ccde ("pps: serial clients support")
Cc: stable@vger.kernel.org
Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
---
 drivers/pps/clients/pps-ldisc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pps/clients/pps-ldisc.c b/drivers/pps/clients/pps-ldisc.c
index fa5660f3c4b7..54678f20edd5 100644
--- a/drivers/pps/clients/pps-ldisc.c
+++ b/drivers/pps/clients/pps-ldisc.c
@@ -46,6 +46,9 @@ static int pps_tty_open(struct tty_struct *tty)
 	struct pps_device *pps;
 	int ret;

+	if (!capable(CAP_SYS_TIME))
+		return -EPERM;
+
 	info.owner = THIS_MODULE;
 	info.dev = NULL;
 	snprintf(info.name, PPS_MAX_NAME_LEN, "%s%d", drv->driver_name, index);
--
2.43.0