[PATCH 1/2] futex: adjust a futex timeout with a per-timens offset

[PATCH 1/2] futex: adjust a futex timeout with a per-timens offset

[Andrei Vagin]

For all commands except FUTEX_WAIT, timeout is interpreted as an
absolute value. This absolute value is inside the task's time namespace
and has to be converted to the host's time.

Cc: <stable@vger.kernel.org>
Fixes: 5a590f35add9 ("posix-clocks: Wire up clock_gettime() with timens offsets")
Reported-by: Hans van der Laan <j.h.vanderlaan@student.utwente.nl>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 kernel/futex.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index a5876694a60e..9ff2b8c5a506 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -39,6 +39,7 @@
 #include <linux/freezer.h>
 #include <linux/memblock.h>
 #include <linux/fault-inject.h>
+#include <linux/time_namespace.h>
 
 #include <asm/futex.h>
 
@@ -3797,6 +3798,8 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
 		t = timespec64_to_ktime(ts);
 		if (cmd == FUTEX_WAIT)
 			t = ktime_add_safe(ktime_get(), t);
+		else if (!(cmd & FUTEX_CLOCK_REALTIME))
+			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
 		tp = &t;
 	}
 	/*
-- 
2.26.2

[tip: timers/urgent] futex: Adjust futex absolute timeouts with per-timens offset

[tip-bot2 for Andrei Vagin]

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     06764291690f8650a9f96dea42cc0dd4138d47d5
Gitweb:        https://git.kernel.org/tip/06764291690f8650a9f96dea42cc0dd4138d47d5
Author:        Andrei Vagin <avagin@gmail.com>
AuthorDate:    Thu, 15 Oct 2020 00:29:08 -07:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 15 Oct 2020 11:24:04 +02:00

futex: Adjust futex absolute timeouts with per-timens offset

For all commands except FUTEX_WAIT, timeout is interpreted as an absolute
value. This absolute value is inside the task's time namespace and has to
be converted to the host's time.

Fixes: 5a590f35add9 ("posix-clocks: Wire up clock_gettime() with timens offsets")
Reported-by: Hans van der Laan <j.h.vanderlaan@student.utwente.nl>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20201015072909.271426-1-avagin@gmail.com

---
 kernel/futex.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index a587669..9ff2b8c 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -39,6 +39,7 @@
 #include <linux/freezer.h>
 #include <linux/memblock.h>
 #include <linux/fault-inject.h>
+#include <linux/time_namespace.h>
 
 #include <asm/futex.h>
 
@@ -3797,6 +3798,8 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
 		t = timespec64_to_ktime(ts);
 		if (cmd == FUTEX_WAIT)
 			t = ktime_add_safe(ktime_get(), t);
+		else if (!(cmd & FUTEX_CLOCK_REALTIME))
+			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
 		tp = &t;
 	}
 	/*

Re: [PATCH 1/2] futex: adjust a futex timeout with a per-timens offset

[Dmitry Safonov]

On 10/15/20 8:29 AM, Andrei Vagin wrote:
> For all commands except FUTEX_WAIT, timeout is interpreted as an
> absolute value. This absolute value is inside the task's time namespace
> and has to be converted to the host's time.
> 
> Cc: <stable@vger.kernel.org>
> Fixes: 5a590f35add9 ("posix-clocks: Wire up clock_gettime() with timens offsets")
> Reported-by: Hans van der Laan <j.h.vanderlaan@student.utwente.nl>
> Signed-off-by: Andrei Vagin <avagin@gmail.com>[..]
> @@ -3797,6 +3798,8 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
>  		t = timespec64_to_ktime(ts);
>  		if (cmd == FUTEX_WAIT)
>  			t = ktime_add_safe(ktime_get(), t);
> +		else if (!(cmd & FUTEX_CLOCK_REALTIME))
> +			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);

Err, it probably should be
: else if (!(op & FUTEX_CLOCK_REALTIME))

And there's also
: SYSCALL_DEFINE6(futex_time32, ...)
which wants to be patched.

Thanks,
          Dmitry

Re: [PATCH 1/2] futex: adjust a futex timeout with a per-timens offset

[Thomas Gleixner]

On Thu, Oct 15 2020 at 14:26, Dmitry Safonov wrote:

> On 10/15/20 8:29 AM, Andrei Vagin wrote:
>> For all commands except FUTEX_WAIT, timeout is interpreted as an
>> absolute value. This absolute value is inside the task's time namespace
>> and has to be converted to the host's time.
>> 
>> Cc: <stable@vger.kernel.org>
>> Fixes: 5a590f35add9 ("posix-clocks: Wire up clock_gettime() with timens offsets")
>> Reported-by: Hans van der Laan <j.h.vanderlaan@student.utwente.nl>
>> Signed-off-by: Andrei Vagin <avagin@gmail.com>[..]
>> @@ -3797,6 +3798,8 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
>>  		t = timespec64_to_ktime(ts);
>>  		if (cmd == FUTEX_WAIT)
>>  			t = ktime_add_safe(ktime_get(), t);
>> +		else if (!(cmd & FUTEX_CLOCK_REALTIME))
>> +			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
>
> Err, it probably should be
> : else if (!(op & FUTEX_CLOCK_REALTIME))

Duh, you are right. I stared at it for a while and did not spot it.

> And there's also
> : SYSCALL_DEFINE6(futex_time32, ...)
> which wants to be patched.

Indeed. I zapped the commits.

Thanks,

        tglx

Re: [PATCH 1/2] futex: adjust a futex timeout with a per-timens offset

[Andrei Vagin]

On Thu, Oct 15, 2020 at 04:13:42PM +0200, Thomas Gleixner wrote:
> On Thu, Oct 15 2020 at 14:26, Dmitry Safonov wrote:
> 
> > On 10/15/20 8:29 AM, Andrei Vagin wrote:
> >> For all commands except FUTEX_WAIT, timeout is interpreted as an
> >> absolute value. This absolute value is inside the task's time namespace
> >> and has to be converted to the host's time.
> >> 
> >> Cc: <stable@vger.kernel.org>
> >> Fixes: 5a590f35add9 ("posix-clocks: Wire up clock_gettime() with timens offsets")
> >> Reported-by: Hans van der Laan <j.h.vanderlaan@student.utwente.nl>
> >> Signed-off-by: Andrei Vagin <avagin@gmail.com>[..]
> >> @@ -3797,6 +3798,8 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
> >>  		t = timespec64_to_ktime(ts);
> >>  		if (cmd == FUTEX_WAIT)
> >>  			t = ktime_add_safe(ktime_get(), t);
> >> +		else if (!(cmd & FUTEX_CLOCK_REALTIME))
> >> +			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
> >
> > Err, it probably should be
> > : else if (!(op & FUTEX_CLOCK_REALTIME))

Dmitry, thank you for catching this.

> 
> Duh, you are right. I stared at it for a while and did not spot it.
> 
> > And there's also
> > : SYSCALL_DEFINE6(futex_time32, ...)
> > which wants to be patched.
> 
> Indeed. I zapped the commits.

I sent a new version. This time, I extended the test to check
FUTEX_CLOCK_REALTIME and I compiled and run the compat version.
Everything works as it should be.

Thanks,
Andrei