linux-kernel - [PATCH v3 3/5] rtc: Fix the RTC time comparison issues adding cast

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Message-Id: <20250109-enable-rtc-v3-3-f003e8144419@baylibre.com>
Date: Fri, 11 Apr 2025 14:35:56 +0200
From: Alexandre Mergnat <amergnat@...libre.com>
To: Eddie Huang <eddie.huang@...iatek.com>, 
 Sean Wang <sean.wang@...iatek.com>, 
 Alexandre Belloni <alexandre.belloni@...tlin.com>, 
 Matthias Brugger <matthias.bgg@...il.com>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, 
 linux-mediatek@...ts.infradead.org, linux-rtc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
 Alexandre Mergnat <amergnat@...libre.com>
Subject: [PATCH v3 3/5] rtc: Fix the RTC time comparison issues adding cast

The RTC subsystem was experiencing comparison issues between signed and
unsigned time values. When comparing time64_t variables (signed) with
potentially unsigned range values, incorrect results could occur leading
to runtime errors.

Adds explicit type casts to time64_t for critical RTC time comparisons
in both class.c and interface.c files. The changes ensure proper
handling of negative time values during range validation and offset
calculations, particularly when dealing with timestamps before 1970.

The previous implementation might incorrectly interpret negative values
as extremely large positive values, causing unexpected behavior in the
RTC hardware abstraction logic.

Signed-off-by: Alexandre Mergnat <amergnat@...libre.com>
---
 drivers/rtc/class.c     | 6 +++---
 drivers/rtc/interface.c | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index e31fa0ad127e9..1ee3f609f92ea 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -282,7 +282,7 @@ static void rtc_device_get_offset(struct rtc_device *rtc)
 	 * then we can not expand the RTC range by adding or subtracting one
 	 * offset.
 	 */
-	if (rtc->range_min == rtc->range_max)
+	if (rtc->range_min == (time64_t)rtc->range_max)
 		return;
 
 	ret = device_property_read_u32(rtc->dev.parent, "start-year",
@@ -299,7 +299,7 @@ static void rtc_device_get_offset(struct rtc_device *rtc)
 	if (!rtc->set_start_time)
 		return;
 
-	range_secs = rtc->range_max - rtc->range_min + 1;
+	range_secs = (time64_t)rtc->range_max - rtc->range_min + 1;
 
 	/*
 	 * If the start_secs is larger than the maximum seconds (rtc->range_max)
@@ -327,7 +327,7 @@ static void rtc_device_get_offset(struct rtc_device *rtc)
 	 *
 	 * Otherwise the offset seconds should be 0.
 	 */
-	if (rtc->start_secs > rtc->range_max ||
+	if (rtc->start_secs > (time64_t)rtc->range_max ||
 	    rtc->start_secs + range_secs - 1 < rtc->range_min)
 		rtc->offset_secs = rtc->start_secs - rtc->range_min;
 	else if (rtc->start_secs > rtc->range_min)
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index aaf76406cd7d7..93bdf06807f23 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -37,7 +37,7 @@ static void rtc_add_offset(struct rtc_device *rtc, struct rtc_time *tm)
 	 */
 	if ((rtc->start_secs > rtc->range_min && secs >= rtc->start_secs) ||
 	    (rtc->start_secs < rtc->range_min &&
-	     secs <= (rtc->start_secs + rtc->range_max - rtc->range_min)))
+	     secs <= (time64_t)(rtc->start_secs + rtc->range_max - rtc->range_min)))
 		return;
 
 	rtc_time64_to_tm(secs + rtc->offset_secs, tm);
@@ -58,7 +58,7 @@ static void rtc_subtract_offset(struct rtc_device *rtc, struct rtc_time *tm)
 	 * device. Otherwise we need to subtract the offset to make the time
 	 * values are valid for RTC hardware device.
 	 */
-	if (secs >= rtc->range_min && secs <= rtc->range_max)
+	if (secs >= rtc->range_min && secs <= (time64_t)rtc->range_max)
 		return;
 
 	rtc_time64_to_tm(secs - rtc->offset_secs, tm);
@@ -66,7 +66,7 @@ static void rtc_subtract_offset(struct rtc_device *rtc, struct rtc_time *tm)
 
 static int rtc_valid_range(struct rtc_device *rtc, struct rtc_time *tm)
 {
-	if (rtc->range_min != rtc->range_max) {
+	if (rtc->range_min != (time64_t)rtc->range_max) {
 		time64_t time = rtc_tm_to_time64(tm);
 		time64_t range_min = rtc->set_start_time ? rtc->start_secs :
 			rtc->range_min;
@@ -74,7 +74,7 @@ static int rtc_valid_range(struct rtc_device *rtc, struct rtc_time *tm)
 			(rtc->start_secs + rtc->range_max - rtc->range_min) :
 			rtc->range_max;
 
-		if (time < range_min || time > range_max)
+		if (time < range_min || time > (time64_t)range_max)
 			return -ERANGE;
 	}
 

-- 
2.25.1