ptp: correctly disable flags on old ioctls

Commit 4156065 ("PTP: introduce new versions of IOCTLs",
2019-09-13) introduced new versions of the PTP ioctls which actually
validate that the flags are acceptable values.

As part of this, it cleared the flags value using a bitwise
and+negation, in an attempt to prevent the old ioctl from accidentally
enabling new features.

This is incorrect for a couple of reasons. First, it results in
accidentally preventing previously working flags on the request ioctl.
By clearing the "valid" flags, we now no longer allow setting the
enable, rising edge, or falling edge flags.

Second, if we add new additional flags in the future, they must not be
set by the old ioctl. (Since the flag wasn't checked before, we could
potentially break userspace programs which sent garbage flag data.

The correct way to resolve this is to check for and clear all but the
originally valid flags.

Create defines indicating which flags are correctly checked and
interpreted by the original ioctls. Use these to clear any bits which
will not be correctly interpreted by the original ioctls.

In the future, new flags must be added to the VALID_FLAGS macros, but
*not* to the V1_VALID_FLAGS macros. In this way, new features may be
exposed over the v2 ioctls, but without breaking previous userspace
which happened to not clear the flags value properly. The old ioctl will
continue to behave the same way, while the new ioctl gains the benefit
of using the flags fields.

Cc: Richard Cochran <[email protected]>
Cc: Felipe Balbi <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Christopher Hall <[email protected]>
Signed-off-by: Jacob Keller <[email protected]>
Acked-by: Richard Cochran <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: jacob-keller

drivers/ptp/ptp_chardev.c

@@ -155,7 +155,7 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 			err = -EINVAL;
 			break;
 		} else if (cmd == PTP_EXTTS_REQUEST) {
-			req.extts.flags &= ~PTP_EXTTS_VALID_FLAGS;
+			req.extts.flags &= PTP_EXTTS_V1_VALID_FLAGS;
 			req.extts.rsv[0] = 0;
 			req.extts.rsv[1] = 0;
 		}
@@ -184,7 +184,7 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 			err = -EINVAL;
 			break;
 		} else if (cmd == PTP_PEROUT_REQUEST) {
-			req.perout.flags &= ~PTP_PEROUT_VALID_FLAGS;
+			req.perout.flags &= PTP_PEROUT_V1_VALID_FLAGS;
 			req.perout.rsv[0] = 0;
 			req.perout.rsv[1] = 0;
 			req.perout.rsv[2] = 0;

include/uapi/linux/ptp_clock.h

@@ -31,15 +31,37 @@
 #define PTP_ENABLE_FEATURE (1<<0)
 #define PTP_RISING_EDGE    (1<<1)
 #define PTP_FALLING_EDGE   (1<<2)
+
+/*
+ * flag fields valid for the new PTP_EXTTS_REQUEST2 ioctl.
+ */
 #define PTP_EXTTS_VALID_FLAGS	(PTP_ENABLE_FEATURE |	\
 				 PTP_RISING_EDGE |	\
 				 PTP_FALLING_EDGE)
 
+/*
+ * flag fields valid for the original PTP_EXTTS_REQUEST ioctl.
+ * DO NOT ADD NEW FLAGS HERE.
+ */
+#define PTP_EXTTS_V1_VALID_FLAGS	(PTP_ENABLE_FEATURE |	\
+					 PTP_RISING_EDGE |	\
+					 PTP_FALLING_EDGE)
+
 /*
  * Bits of the ptp_perout_request.flags field:
  */
 #define PTP_PEROUT_ONE_SHOT (1<<0)
+
+/*
+ * flag fields valid for the new PTP_PEROUT_REQUEST2 ioctl.
+ */
 #define PTP_PEROUT_VALID_FLAGS	(PTP_PEROUT_ONE_SHOT)
+
+/*
+ * No flags are valid for the original PTP_PEROUT_REQUEST ioctl
+ */
+#define PTP_PEROUT_V1_VALID_FLAGS	(0)
+
 /*
  * struct ptp_clock_time - represents a time value
  *