[PATCH] ppdev: prevent overflow when setting port timeout

[Linmao Li]

PPSETTIME64 supplies the timeval fields as s64 values, but
pp_set_timeout() narrows tv_usec to int and calculates tv_sec * HZ in a
signed long. Large positive values can therefore be truncated or overflow
and install an unintended timeout.

Keep both fields as s64, reject a non-canonical microsecond value, and
use timespec64_to_jiffies() to cap excessively large timeouts at
MAX_JIFFY_OFFSET. This is a behavior change because both PPSETTIME
ioctls could previously accept values with tv_usec >= USEC_PER_SEC.
The validation follows the precedent set by sock_set_timeout().

Fixes: 3b9ab374a1e6 ("ppdev: convert to y2038 safe")
Signed-off-by: Linmao Li <lilinmao@xxxxxxxxxx>
---
 drivers/char/ppdev.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/char/ppdev.c b/drivers/char/ppdev.c
index 6da817b9849f..8803268b4cdc 100644
--- a/drivers/char/ppdev.c
+++ b/drivers/char/ppdev.c
@@ -340,15 +340,17 @@ static enum ieee1284_phase init_phase(int mode)
 	return IEEE1284_PH_FWD_IDLE;
 }
 
-static int pp_set_timeout(struct pardevice *pdev, long tv_sec, int tv_usec)
+static int pp_set_timeout(struct pardevice *pdev, s64 tv_sec, s64 tv_usec)
 {
+	struct timespec64 ts;
 	long to_jiffies;
 
-	if ((tv_sec < 0) || (tv_usec < 0))
+	if (tv_sec < 0 || tv_usec < 0 || tv_usec >= USEC_PER_SEC)
 		return -EINVAL;
 
-	to_jiffies = usecs_to_jiffies(tv_usec);
-	to_jiffies += tv_sec * HZ;
+	ts.tv_sec = tv_sec;
+	ts.tv_nsec = tv_usec * NSEC_PER_USEC;
+	to_jiffies = timespec64_to_jiffies(&ts);
 	if (to_jiffies <= 0)
 		return -EINVAL;
 
-- 
2.25.1