[PATCH v5 0/4] libuuid: Fix pre-1970 UUID timestamp overflow

[PATCH v5 0/4] libuuid: Fix pre-1970 UUID timestamp overflow

[Kiran Rangoon]

> On 2025-12-18 16:31:21-0500, Kiran Rangoon wrote:
> > I revised the code in response to your feedback.

> Thanks!

> > > Looking at this more closely: __uuid_time() is directly exposed to users
> > > of libuuid as uuid_time(). This means that any change of the function's
> > > contract would break all external users and should be avoided at all
> > > costs.
> >
> > Reversed the change there.
> 
> Your new revision is based on top of your old series.
> Instead it should always be based on upstream code.
> In this case the util-linux master branch.

Fixed in v4: I rebased directly on origin/master instead of building
on my previous patch series.
>
> > > Fortunately it turns out that the timestamps embedded in UUIDs
> > > only use 60 bits. This means that the calculation can be performed in an
> > > int64_t without any risk of over- or underflow. Please try to implement
> > > it that way instead.
> >
> > I'm using signed int64_t here as suggested.
> >
> > > It might be useful to change the signature of gregorian_to_unix() to
> > > "static void gregorian_to_unix(uint64_t ts, struct timeval *tv)".
> >
> > I revised the code to use a struct timeval now.
>
> That looks good. However that refactoring should be in its own commit.
> More on that below.

Fixed in v4: The refactoring is now in its own dedicated commit (patch 2/4).
>
> > > Also please perform each logical step in a dedicated commit.
> >
> > > I made two commits, one for the code change and the other for tests, but
> > > if there is a way you would perfer me to do it I could change it.
> >
> The test is a bad candidate to split out. After each commit the
> repository needs to be in a consistent state, which means that the code
> builds and the tests pass. As the code change breaks the existing test,
> the test needs to be adapted in lockstep.

Understood. In v4, the test updates are included with the code changes
that require them, maintaining repository consistency at each commit.
>
> I see the following commits:
>
> 1) Switch to the simpler constant definition
> 2) Pass 'struct timeval' to gregorian_to_unix()
> 3) Fix the overflow, adapt the existing test
> 4) Add a hand full of additional testcases.

Implemented exactly as suggested in v4.

> Also this patch now lost its useful commit message which got replaced by
> our discussion. This should not happen. Each commit should explain why
> it is being done.

Fixed in v4: All commits now have proper descriptive messages explaining
the rationale for each change.
>
> > +     const uint64_t offset = 0x01B21DD213814000ULL;
> > +     int64_t t = (int64_t) ts - (int64_t) offset;
>
> Whitespace corruption?

Fixed in v4: Proper tab indentation is used throughout.
---

This v4 patch series addresses all the feedback points above:

Kiran Rangoon (4):
  libuuid: simplify gregorian-to-unix offset calculation
  libuuid: refactor gregorian_to_unix to populate timeval directly
  libuuid: fix timestamp overflow for pre-1970 dates
  tests: correct UUID timestamp test expectations

 libuuid/src/uuid_time.c       | 15 +++++++--------
 tests/expected/uuid/uuidparse |  5 ++++-
 tests/ts/uuid/uuidparse       |  3 +++
 3 files changed, 14 insertions(+), 9 deletions(-)

-- 
2.47.3

[PATCH v5 1/4] libuuid: simplify gregorian-to-unix offset calculation

[Kiran Rangoon]

Replace complex bit-shift offset calculation with a simple constant
definition for better readability and maintainability.

Signed-off-by: Kiran Rangoon <kiranrangoon0@gmail.com>
---
 libuuid/src/uuid_time.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libuuid/src/uuid_time.c b/libuuid/src/uuid_time.c
index c7516152b..e2b991d74 100644
--- a/libuuid/src/uuid_time.c
+++ b/libuuid/src/uuid_time.c
@@ -62,7 +62,8 @@ time_t __uuid_time(const uuid_t uu, struct timeval *ret_tv);
 
 static uint64_t gregorian_to_unix(uint64_t ts)
 {
-	return ts - ((((uint64_t) 0x01B21DD2) << 32) + 0x13814000);
+	const uint64_t offset = 0x01B21DD213814000ULL;
+	return ts - offset;
 }
 
 static void uuid_time_v1(const struct uuid *uuid, struct timeval *tv)
-- 
2.47.3

[PATCH v5 2/4] libuuid: refactor gregorian_to_unix to populate timeval directly

[Kiran Rangoon]

Change function signature to take struct timeval pointer and populate
it directly, eliminating duplicate conversion code in callers.

Signed-off-by: Kiran Rangoon <kiranrangoon0@gmail.com>
---
 libuuid/src/uuid_time.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/libuuid/src/uuid_time.c b/libuuid/src/uuid_time.c
index e2b991d74..2f7c6652c 100644
--- a/libuuid/src/uuid_time.c
+++ b/libuuid/src/uuid_time.c
@@ -60,10 +60,12 @@
 /* prototype to make compiler happy */
 time_t __uuid_time(const uuid_t uu, struct timeval *ret_tv);
 
-static uint64_t gregorian_to_unix(uint64_t ts)
+static void gregorian_to_unix(uint64_t ts, struct timeval *tv)
 {
 	const uint64_t offset = 0x01B21DD213814000ULL;
-	return ts - offset;
+	uint64_t clock_reg = ts - offset;
+	tv->tv_sec = clock_reg / 10000000;
+	tv->tv_usec = (clock_reg % 10000000) / 10;
 }
 
 static void uuid_time_v1(const struct uuid *uuid, struct timeval *tv)
@@ -74,9 +76,7 @@ static void uuid_time_v1(const struct uuid *uuid, struct timeval *tv)
 	high = uuid->time_mid | ((uuid->time_hi_and_version & 0xFFF) << 16);
 	clock_reg = uuid->time_low | ((uint64_t) high << 32);
 
-	clock_reg = gregorian_to_unix(clock_reg);
-	tv->tv_sec = clock_reg / 10000000;
-	tv->tv_usec = (clock_reg % 10000000) / 10;
+	gregorian_to_unix(clock_reg, tv);
 }
 
 static void uuid_time_v6(const struct uuid *uuid, struct timeval *tv)
@@ -89,9 +89,7 @@ static void uuid_time_v6(const struct uuid *uuid, struct timeval *tv)
 	clock_reg <<= 12;
 	clock_reg |= uuid->time_hi_and_version & 0xFFF;
 
-	clock_reg = gregorian_to_unix(clock_reg);
-	tv->tv_sec = clock_reg / 10000000;
-	tv->tv_usec = (clock_reg % 10000000) / 10;
+	gregorian_to_unix(clock_reg, tv);
 }
 
 static void uuid_time_v7(const struct uuid *uuid, struct timeval *tv)
-- 
2.47.3

[PATCH v5 3/4] libuuid: fix timestamp overflow for pre-1970 dates

[Kiran Rangoon]

Use int64_t arithmetic to correctly handle timestamps before Unix epoch.
This fixes the overflow that was causing UUID timestamps from 1582 to
appear as far-future dates. Update test expectations accordingly.

Signed-off-by: Kiran Rangoon <kiranrangoon0@gmail.com>
---
 libuuid/src/uuid_time.c       | 2 +-
 tests/expected/uuid/uuidparse | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libuuid/src/uuid_time.c b/libuuid/src/uuid_time.c
index 2f7c6652c..63179fd76 100644
--- a/libuuid/src/uuid_time.c
+++ b/libuuid/src/uuid_time.c
@@ -63,7 +63,7 @@ time_t __uuid_time(const uuid_t uu, struct timeval *ret_tv);
 static void gregorian_to_unix(uint64_t ts, struct timeval *tv)
 {
 	const uint64_t offset = 0x01B21DD213814000ULL;
-	uint64_t clock_reg = ts - offset;
+	int64_t clock_reg = (int64_t)(ts - offset);
 	tv->tv_sec = clock_reg / 10000000;
 	tv->tv_usec = (clock_reg % 10000000) / 10;
 }
diff --git a/tests/expected/uuid/uuidparse b/tests/expected/uuid/uuidparse
index 9edb05e4e..e44964b30 100644
--- a/tests/expected/uuid/uuidparse
+++ b/tests/expected/uuid/uuidparse
@@ -11,7 +11,7 @@ UUID                                  VARIANT   TYPE       TIME
 00000000-0000-3000-8000-000000000000  DCE       name-based 
 00000000-0000-4000-8000-000000000000  DCE       random     
 00000000-0000-5000-8000-000000000000  DCE       sha1-based 
-00000000-0000-6000-8000-000000000000  DCE       time-v6    60038-03-11 05:36:10,955161+00:00
+00000000-0000-6000-8000-000000000000  DCE       time-v6    1582-10-15 00:00:00,000000+00:00
 00000000-0000-0000-d000-000000000000  Microsoft            
 00000000-0000-1000-d000-000000000000  Microsoft            
 00000000-0000-2000-d000-000000000000  Microsoft            
-- 
2.47.3

[PATCH v5 4/4] tests: correct UUID timestamp test expectations

[Kiran Rangoon]

Update expected timestamps for additional test UUIDs to match actual
output. These test cases provide coverage for various timestamp ranges
including pre-epoch, historical, and far-future dates.

Signed-off-by: Kiran Rangoon <kiranrangoon0@gmail.com>
---
 tests/expected/uuid/uuidparse | 3 +++
 tests/ts/uuid/uuidparse       | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/tests/expected/uuid/uuidparse b/tests/expected/uuid/uuidparse
index e44964b30..61b49ef66 100644
--- a/tests/expected/uuid/uuidparse
+++ b/tests/expected/uuid/uuidparse
@@ -29,6 +29,9 @@ UUID                                  VARIANT   TYPE       TIME
 9b274c46-544a-11e7-a972-00037f500001  DCE       time-based 2017-06-18 17:21:46,544647+00:00
 1ec9414c-232a-6b00-b3c8-9f6bdeced846  DCE       time-v6    2022-02-22 19:22:22,000000+00:00
 017f22e2-79b2-7cc3-98c4-dc0c0c07398f  DCE       time-v7    2022-02-22 19:22:22,002000+00:00
+bf2eb110-d788-1003-aa59-ce1e9e293641  DCE       time-based 1586-03-19 15:05:26,3611398+00:00
+f81d4fae-7dec-11d0-a765-00a0c91e6bf6  DCE       time-based 1997-02-03 17:43:12,216875+00:00
+01234567-89ab-1def-8000-123456789abc  DCE       time-based 4764-11-18 19:35:47,841162+00:00
 5c146b14-3c52-8afd-938a-375d0df1fbf6  DCE       vendor     
 invalid-input                         invalid   invalid    invalid
 return value: 0
diff --git a/tests/ts/uuid/uuidparse b/tests/ts/uuid/uuidparse
index 2903ce56d..f131986ba 100755
--- a/tests/ts/uuid/uuidparse
+++ b/tests/ts/uuid/uuidparse
@@ -56,6 +56,9 @@ echo '00000000-0000-0000-0000-000000000000
 9b274c46-544a-11e7-a972-00037f500001
 1ec9414c-232a-6b00-b3c8-9f6bdeced846
 017f22e2-79b2-7cc3-98c4-dc0c0c07398f
+bf2eb110-d788-1003-aa59-ce1e9e293641
+f81d4fae-7dec-11d0-a765-00a0c91e6bf6
+01234567-89ab-1def-8000-123456789abc
 5c146b14-3c52-8afd-938a-375d0df1fbf6
 
 invalid-input' | $TS_CMD_UUIDPARSE >> $TS_OUTPUT 2>> $TS_ERRLOG
-- 
2.47.3

Re: [PATCH v5 0/4] libuuid: Fix pre-1970 UUID timestamp overflow

[Karel Zak]

On Sun, Dec 28, 2025 at 10:50:56PM -0500, Kiran Rangoon wrote:
> Kiran Rangoon (4):
>   libuuid: simplify gregorian-to-unix offset calculation
>   libuuid: refactor gregorian_to_unix to populate timeval directly
>   libuuid: fix timestamp overflow for pre-1970 dates
>   tests: correct UUID timestamp test expectations

Applied (from PR created by Thomas). Thanks to both for all the work!

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com