[PATCH v2] system/rtc: Fix a possible year-2038 integer overflow problem

[PATCH v2] system/rtc: Fix a possible year-2038 integer overflow problem

[Thomas Huth]

From: Thomas Huth <thuth@redhat.com>

rtc_realtime_clock_offset is initialized with:

  rtc_realtime_clock_offset = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;

And QEMU_CLOCK_REALTIME might be based on gettimeofday() in certain
cases (see get_clock_realtime() in include/qemu/timer.h). So this
counter will exceed 32 bits in the year 2038, thus we should not
store this value in a normal integer variable. Change it to a time_t
to fix the problem.
And while we're at it, also adjust the nearby rtc_host_datetime_offset
variable to be on the safe side in the related code.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 v2: Use time_t instead of int64_t

 system/rtc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/system/rtc.c b/system/rtc.c
index f13dd392a76..018609a4f9a 100644
--- a/system/rtc.c
+++ b/system/rtc.c
@@ -41,8 +41,8 @@ static enum {
     RTC_BASE_DATETIME,
 } rtc_base_type = RTC_BASE_UTC;
 static time_t rtc_ref_start_datetime;
-static int rtc_realtime_clock_offset; /* used only with QEMU_CLOCK_REALTIME */
-static int rtc_host_datetime_offset = -1; /* valid & used only with
+static time_t rtc_realtime_clock_offset; /* used only with QEMU_CLOCK_REALTIME */
+static time_t rtc_host_datetime_offset = -1; /* valid & used only with
                                              RTC_BASE_DATETIME */
 QEMUClockType rtc_clock;
 /***********************************************************/
-- 
2.54.0

Re: [PATCH v2] system/rtc: Fix a possible year-2038 integer overflow problem

[Daniel P. Berrangé]

On Mon, May 18, 2026 at 06:34:08PM +0200, Thomas Huth wrote:
> From: Thomas Huth <thuth@redhat.com>
> 
> rtc_realtime_clock_offset is initialized with:
> 
>   rtc_realtime_clock_offset = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
> 
> And QEMU_CLOCK_REALTIME might be based on gettimeofday() in certain
> cases (see get_clock_realtime() in include/qemu/timer.h). So this
> counter will exceed 32 bits in the year 2038, thus we should not
> store this value in a normal integer variable. Change it to a time_t
> to fix the problem.
> And while we're at it, also adjust the nearby rtc_host_datetime_offset
> variable to be on the safe side in the related code.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  v2: Use time_t instead of int64_t
> 
>  system/rtc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
-- 
|: https://berrange.com       ~~        https://hachyderm.io/@berrange :|
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Re: [PATCH v2] system/rtc: Fix a possible year-2038 integer overflow problem

[Laurent Vivier]

Le 18/05/2026 à 18:34, Thomas Huth a écrit :
> From: Thomas Huth <thuth@redhat.com>
> 
> rtc_realtime_clock_offset is initialized with:
> 
>    rtc_realtime_clock_offset = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
> 
> And QEMU_CLOCK_REALTIME might be based on gettimeofday() in certain
> cases (see get_clock_realtime() in include/qemu/timer.h). So this
> counter will exceed 32 bits in the year 2038, thus we should not
> store this value in a normal integer variable. Change it to a time_t
> to fix the problem.
> And while we're at it, also adjust the nearby rtc_host_datetime_offset
> variable to be on the safe side in the related code.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   v2: Use time_t instead of int64_t
> 
>   system/rtc.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/system/rtc.c b/system/rtc.c
> index f13dd392a76..018609a4f9a 100644
> --- a/system/rtc.c
> +++ b/system/rtc.c
> @@ -41,8 +41,8 @@ static enum {
>       RTC_BASE_DATETIME,
>   } rtc_base_type = RTC_BASE_UTC;
>   static time_t rtc_ref_start_datetime;
> -static int rtc_realtime_clock_offset; /* used only with QEMU_CLOCK_REALTIME */
> -static int rtc_host_datetime_offset = -1; /* valid & used only with
> +static time_t rtc_realtime_clock_offset; /* used only with QEMU_CLOCK_REALTIME */
> +static time_t rtc_host_datetime_offset = -1; /* valid & used only with
>                                                RTC_BASE_DATETIME */
>   QEMUClockType rtc_clock;
>   /***********************************************************/

Reviewed-by: Laurent Vivier <laurent@vivier.eu>