Currently, the lockdown state is queried unconditionally, even though
its result is used only if the PERF_SAMPLE_REGS_INTR bit is set in
attr.sample_type. While that doesn't matter in case of the Lockdown LSM,
it causes trouble with the SELinux's lockdown hook implementation.
SELinux implements the locked_down hook with a check whether the current
task's type has the corresponding "lockdown" class permission
("integrity" or "confidentiality") allowed in the policy. This means
that calling the hook when the access control decision would be ignored
generates a bogus permission check and audit record.
Fix this by checking sample_type first and only calling the hook when
its result would be honored.
Fixes: b0c8fdc7fdb7 ("lockdown: Lock down perf when in confidentiality mode")
Signed-off-by: Ondrej Mosnacek <[email protected]>
---
kernel/events/core.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 129dee540a8b..0f857307e9bd 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11796,12 +11796,12 @@ SYSCALL_DEFINE5(perf_event_open,
return err;
}
- err = security_locked_down(LOCKDOWN_PERF);
- if (err && (attr.sample_type & PERF_SAMPLE_REGS_INTR))
- /* REGS_INTR can leak data, lockdown must prevent this */
- return err;
-
- err = 0;
+ /* REGS_INTR can leak data, lockdown must prevent this */
+ if (attr.sample_type & PERF_SAMPLE_REGS_INTR) {
+ err = security_locked_down(LOCKDOWN_PERF);
+ if (err)
+ return err;
+ }
/*
* In cgroup mode, the pid argument is used to pass the fd
--
2.29.2
On Tue, Mar 16, 2021 at 10:30 AM Peter Zijlstra <[email protected]> wrote:
> On Tue, Mar 16, 2021 at 09:53:21AM -0400, Paul Moore wrote:
> > On Wed, Feb 24, 2021 at 4:59 PM Ondrej Mosnacek <[email protected]> wrote:
> > >
> > > Currently, the lockdown state is queried unconditionally, even though
> > > its result is used only if the PERF_SAMPLE_REGS_INTR bit is set in
> > > attr.sample_type. While that doesn't matter in case of the Lockdown LSM,
> > > it causes trouble with the SELinux's lockdown hook implementation.
> > >
> > > SELinux implements the locked_down hook with a check whether the current
> > > task's type has the corresponding "lockdown" class permission
> > > ("integrity" or "confidentiality") allowed in the policy. This means
> > > that calling the hook when the access control decision would be ignored
> > > generates a bogus permission check and audit record.
> > >
> > > Fix this by checking sample_type first and only calling the hook when
> > > its result would be honored.
> > >
> > > Fixes: b0c8fdc7fdb7 ("lockdown: Lock down perf when in confidentiality mode")
> > > Signed-off-by: Ondrej Mosnacek <[email protected]>
> > > ---
> > > kernel/events/core.c | 12 ++++++------
> > > 1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > Perf/core folks, do you want to pull this in via your tree? If I
> > don't hear anything in the next day I'll pull this in via the
> > selinux/next tree.
> >
> > Reviewed-by: Paul Moore <[email protected]>
>
> Ah, fell in the cracks... I've no idea what Changelog is trying to tell
> me. It is pure gibberish to me. But the patch seems harmless enough to me.
>
> Let me queue it then.
Great, thanks.
--
paul moore
http://www.paul-moore.com
On Wed, Feb 24, 2021 at 4:59 PM Ondrej Mosnacek <[email protected]> wrote:
>
> Currently, the lockdown state is queried unconditionally, even though
> its result is used only if the PERF_SAMPLE_REGS_INTR bit is set in
> attr.sample_type. While that doesn't matter in case of the Lockdown LSM,
> it causes trouble with the SELinux's lockdown hook implementation.
>
> SELinux implements the locked_down hook with a check whether the current
> task's type has the corresponding "lockdown" class permission
> ("integrity" or "confidentiality") allowed in the policy. This means
> that calling the hook when the access control decision would be ignored
> generates a bogus permission check and audit record.
>
> Fix this by checking sample_type first and only calling the hook when
> its result would be honored.
>
> Fixes: b0c8fdc7fdb7 ("lockdown: Lock down perf when in confidentiality mode")
> Signed-off-by: Ondrej Mosnacek <[email protected]>
> ---
> kernel/events/core.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
Perf/core folks, do you want to pull this in via your tree? If I
don't hear anything in the next day I'll pull this in via the
selinux/next tree.
Reviewed-by: Paul Moore <[email protected]>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 129dee540a8b..0f857307e9bd 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -11796,12 +11796,12 @@ SYSCALL_DEFINE5(perf_event_open,
> return err;
> }
>
> - err = security_locked_down(LOCKDOWN_PERF);
> - if (err && (attr.sample_type & PERF_SAMPLE_REGS_INTR))
> - /* REGS_INTR can leak data, lockdown must prevent this */
> - return err;
> -
> - err = 0;
> + /* REGS_INTR can leak data, lockdown must prevent this */
> + if (attr.sample_type & PERF_SAMPLE_REGS_INTR) {
> + err = security_locked_down(LOCKDOWN_PERF);
> + if (err)
> + return err;
> + }
>
> /*
> * In cgroup mode, the pid argument is used to pass the fd
> --
> 2.29.2
--
paul moore
http://www.paul-moore.com
On Tue, Mar 16, 2021 at 09:53:21AM -0400, Paul Moore wrote:
> On Wed, Feb 24, 2021 at 4:59 PM Ondrej Mosnacek <[email protected]> wrote:
> >
> > Currently, the lockdown state is queried unconditionally, even though
> > its result is used only if the PERF_SAMPLE_REGS_INTR bit is set in
> > attr.sample_type. While that doesn't matter in case of the Lockdown LSM,
> > it causes trouble with the SELinux's lockdown hook implementation.
> >
> > SELinux implements the locked_down hook with a check whether the current
> > task's type has the corresponding "lockdown" class permission
> > ("integrity" or "confidentiality") allowed in the policy. This means
> > that calling the hook when the access control decision would be ignored
> > generates a bogus permission check and audit record.
> >
> > Fix this by checking sample_type first and only calling the hook when
> > its result would be honored.
> >
> > Fixes: b0c8fdc7fdb7 ("lockdown: Lock down perf when in confidentiality mode")
> > Signed-off-by: Ondrej Mosnacek <[email protected]>
> > ---
> > kernel/events/core.c | 12 ++++++------
> > 1 file changed, 6 insertions(+), 6 deletions(-)
>
> Perf/core folks, do you want to pull this in via your tree? If I
> don't hear anything in the next day I'll pull this in via the
> selinux/next tree.
>
> Reviewed-by: Paul Moore <[email protected]>
Ah, fell in the cracks... I've no idea what Changelog is trying to tell
me. It is pure gibberish to me. But the patch seems harmless enough to me.
Let me queue it then.
The following commit has been merged into the perf/core branch of tip:
Commit-ID: 08ef1af4de5fe7de9c6d69f1e22e51b66e385d9b
Gitweb: https://git.kernel.org/tip/08ef1af4de5fe7de9c6d69f1e22e51b66e385d9b
Author: Ondrej Mosnacek <[email protected]>
AuthorDate: Wed, 24 Feb 2021 22:56:28 +01:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Tue, 16 Mar 2021 21:44:43 +01:00
perf/core: Fix unconditional security_locked_down() call
Currently, the lockdown state is queried unconditionally, even though
its result is used only if the PERF_SAMPLE_REGS_INTR bit is set in
attr.sample_type. While that doesn't matter in case of the Lockdown LSM,
it causes trouble with the SELinux's lockdown hook implementation.
SELinux implements the locked_down hook with a check whether the current
task's type has the corresponding "lockdown" class permission
("integrity" or "confidentiality") allowed in the policy. This means
that calling the hook when the access control decision would be ignored
generates a bogus permission check and audit record.
Fix this by checking sample_type first and only calling the hook when
its result would be honored.
Fixes: b0c8fdc7fdb7 ("lockdown: Lock down perf when in confidentiality mode")
Signed-off-by: Ondrej Mosnacek <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Paul Moore <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
kernel/events/core.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6182cb1..f079431 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11833,12 +11833,12 @@ SYSCALL_DEFINE5(perf_event_open,
return err;
}
- err = security_locked_down(LOCKDOWN_PERF);
- if (err && (attr.sample_type & PERF_SAMPLE_REGS_INTR))
- /* REGS_INTR can leak data, lockdown must prevent this */
- return err;
-
- err = 0;
+ /* REGS_INTR can leak data, lockdown must prevent this */
+ if (attr.sample_type & PERF_SAMPLE_REGS_INTR) {
+ err = security_locked_down(LOCKDOWN_PERF);
+ if (err)
+ return err;
+ }
/*
* In cgroup mode, the pid argument is used to pass the fd