[PATCH] ptp: guard ptp_clock_gettime() if neither gettimex64 nor

[Junjie Cao <junjie.cao@intel.com>]

Syzbot reports a NULL function pointer call on arm64 when
ptp_clock_gettime() falls back to ->gettime64() and the driver provides
neither ->gettimex64() nor ->gettime64(). This leads to a crash in the
posix clock gettime path.

Return -EOPNOTSUPP when both callbacks are missing, avoiding the crash
and matching the defensive style used in the posix clock layer.

Reported-by: syzbot+c8c0e7ccabd456541612@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c8c0e7ccabd456541612
Signed-off-by: Junjie Cao <junjie.cao@intel.com>
---
 drivers/ptp/ptp_clock.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(
diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index ef020599b771..764bd25220c1 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -110,12 +110,14 @@ static int ptp_clock_settime(struct posix_clock *pc, const struct timespec64 *tp
 static int ptp_clock_gettime(struct posix_clock *pc, struct timespec64 *tp)
 {
 	struct ptp_clock *ptp = container_of(pc, struct ptp_clock, clock);
-	int err;
+	int err = -EOPNOTSUPP;
 
 	if (ptp->info->gettimex64)
-		err = ptp->info->gettimex64(ptp->info, tp, NULL);
-	else
-		err = ptp->info->gettime64(ptp->info, tp);
+		return ptp->info->gettimex64(ptp->info, tp, NULL);
+
+	if (ptp->info->gettime64)
+		return ptp->info->gettime64(ptp->info, tp);
+
 	return err;
 }
 
-- 
2.43.0