ipc: don't audit capability check in ipc_permissions()

[PATCH] ipc: don't audit capability check in ipc_permissions()

Posted by Ondrej Mosnacek 2 weeks, 2 days ago

The IPC sysctls implement the ctl_table_root::permissions hook and
they override the file access mode based on the CAP_CHECKPOINT_RESTORE
capability, which is being checked regardless of whether any access is
actually denied or not, so if an LSM denies the capability, an audit
record may be logged even when access is in fact granted.

It wouldn't be viable to restructure the sysctl permission logic to only
check the capability when the access would be actually denied if it's
not granted. Thus, do the same as in net_ctl_permissions()
(net/sysctl_net.c) - switch from ns_capable() to ns_capable_noaudit(),
so that the check never emits an audit record.

Fixes: 0889f44e2810 ("ipc: Check permissions for checkpoint_restart sysctls at open time")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
---
 include/linux/capability.h | 6 ++++++
 ipc/ipc_sysctl.c           | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 1fb08922552c7..37db92b3d6f89 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -203,6 +203,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
 		ns_capable(ns, CAP_SYS_ADMIN);
 }
 
+static inline bool checkpoint_restore_ns_capable_noaudit(struct user_namespace *ns)
+{
+	return ns_capable_noaudit(ns, CAP_CHECKPOINT_RESTORE) ||
+		ns_capable_noaudit(ns, CAP_SYS_ADMIN);
+}
+
 /* audit system wants to get cap info from files as well */
 int get_vfs_caps_from_disk(struct mnt_idmap *idmap,
 			   const struct dentry *dentry,
diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index 15b17e86e198c..9b087ebeb643b 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -214,7 +214,7 @@ static int ipc_permissions(struct ctl_table_header *head, const struct ctl_table
 	if (((table->data == &ns->ids[IPC_SEM_IDS].next_id) ||
 	     (table->data == &ns->ids[IPC_MSG_IDS].next_id) ||
 	     (table->data == &ns->ids[IPC_SHM_IDS].next_id)) &&
-	    checkpoint_restore_ns_capable(ns->user_ns))
+	    checkpoint_restore_ns_capable_noaudit(ns->user_ns))
 		mode = 0666;
 	else
 #endif
-- 
2.52.0

Re: [PATCH] ipc: don't audit capability check in ipc_permissions()

Posted by Paul Moore 1 week, 4 days ago

On Thu, Jan 22, 2026 at 9:56 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
>
> The IPC sysctls implement the ctl_table_root::permissions hook and
> they override the file access mode based on the CAP_CHECKPOINT_RESTORE
> capability, which is being checked regardless of whether any access is
> actually denied or not, so if an LSM denies the capability, an audit
> record may be logged even when access is in fact granted.
>
> It wouldn't be viable to restructure the sysctl permission logic to only
> check the capability when the access would be actually denied if it's
> not granted. Thus, do the same as in net_ctl_permissions()
> (net/sysctl_net.c) - switch from ns_capable() to ns_capable_noaudit(),
> so that the check never emits an audit record.
>
> Fixes: 0889f44e2810 ("ipc: Check permissions for checkpoint_restart sysctls at open time")
> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> ---
>  include/linux/capability.h | 6 ++++++
>  ipc/ipc_sysctl.c           | 2 +-
>  2 files changed, 7 insertions(+), 1 deletion(-)

This change seems reasonable to me, but I would make sure Serge has a
chance to review/ACK this patch as it has a capability impact.

-- 
paul-moore.com

Re: [PATCH] ipc: don't audit capability check in ipc_permissions()

Posted by Serge E. Hallyn 1 week, 4 days ago

On Mon, Jan 26, 2026 at 05:50:12PM -0500, Paul Moore wrote:
> On Thu, Jan 22, 2026 at 9:56 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> >
> > The IPC sysctls implement the ctl_table_root::permissions hook and
> > they override the file access mode based on the CAP_CHECKPOINT_RESTORE
> > capability, which is being checked regardless of whether any access is
> > actually denied or not, so if an LSM denies the capability, an audit
> > record may be logged even when access is in fact granted.
> >
> > It wouldn't be viable to restructure the sysctl permission logic to only
> > check the capability when the access would be actually denied if it's
> > not granted. Thus, do the same as in net_ctl_permissions()
> > (net/sysctl_net.c) - switch from ns_capable() to ns_capable_noaudit(),
> > so that the check never emits an audit record.
> >
> > Fixes: 0889f44e2810 ("ipc: Check permissions for checkpoint_restart sysctls at open time")
> > Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> > ---
> >  include/linux/capability.h | 6 ++++++
> >  ipc/ipc_sysctl.c           | 2 +-
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> This change seems reasonable to me, but I would make sure Serge has a
> chance to review/ACK this patch as it has a capability impact.

Acked-by: Serge Hallyn <serge@hallyn.com>

Thanks - looks good to me.

Re: [PATCH] ipc: don't audit capability check in ipc_permissions()

Posted by Paul Moore 1 week, 3 days ago

On Mon, Jan 26, 2026 at 9:01 PM Serge E. Hallyn <serge@hallyn.com> wrote:
> On Mon, Jan 26, 2026 at 05:50:12PM -0500, Paul Moore wrote:
> > On Thu, Jan 22, 2026 at 9:56 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> > >
> > > The IPC sysctls implement the ctl_table_root::permissions hook and
> > > they override the file access mode based on the CAP_CHECKPOINT_RESTORE
> > > capability, which is being checked regardless of whether any access is
> > > actually denied or not, so if an LSM denies the capability, an audit
> > > record may be logged even when access is in fact granted.
> > >
> > > It wouldn't be viable to restructure the sysctl permission logic to only
> > > check the capability when the access would be actually denied if it's
> > > not granted. Thus, do the same as in net_ctl_permissions()
> > > (net/sysctl_net.c) - switch from ns_capable() to ns_capable_noaudit(),
> > > so that the check never emits an audit record.
> > >
> > > Fixes: 0889f44e2810 ("ipc: Check permissions for checkpoint_restart sysctls at open time")
> > > Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> > > ---
> > >  include/linux/capability.h | 6 ++++++
> > >  ipc/ipc_sysctl.c           | 2 +-
> > >  2 files changed, 7 insertions(+), 1 deletion(-)
> >
> > This change seems reasonable to me, but I would make sure Serge has a
> > chance to review/ACK this patch as it has a capability impact.
>
> Acked-by: Serge Hallyn <serge@hallyn.com>
>
> Thanks - looks good to me.

I don't see a dedicated IPC maintainer/tree, do you want to take this
via the capabilities tree Serge?

-- 
paul-moore.com

Re: [PATCH] ipc: don't audit capability check in ipc_permissions()

Posted by Serge E. Hallyn 1 week, 3 days ago

On Tue, Jan 27, 2026 at 05:06:47PM -0500, Paul Moore wrote:
> On Mon, Jan 26, 2026 at 9:01 PM Serge E. Hallyn <serge@hallyn.com> wrote:
> > On Mon, Jan 26, 2026 at 05:50:12PM -0500, Paul Moore wrote:
> > > On Thu, Jan 22, 2026 at 9:56 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> > > >
> > > > The IPC sysctls implement the ctl_table_root::permissions hook and
> > > > they override the file access mode based on the CAP_CHECKPOINT_RESTORE
> > > > capability, which is being checked regardless of whether any access is
> > > > actually denied or not, so if an LSM denies the capability, an audit
> > > > record may be logged even when access is in fact granted.
> > > >
> > > > It wouldn't be viable to restructure the sysctl permission logic to only
> > > > check the capability when the access would be actually denied if it's
> > > > not granted. Thus, do the same as in net_ctl_permissions()
> > > > (net/sysctl_net.c) - switch from ns_capable() to ns_capable_noaudit(),
> > > > so that the check never emits an audit record.
> > > >
> > > > Fixes: 0889f44e2810 ("ipc: Check permissions for checkpoint_restart sysctls at open time")
> > > > Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> > > > ---
> > > >  include/linux/capability.h | 6 ++++++
> > > >  ipc/ipc_sysctl.c           | 2 +-
> > > >  2 files changed, 7 insertions(+), 1 deletion(-)
> > >
> > > This change seems reasonable to me, but I would make sure Serge has a
> > > chance to review/ACK this patch as it has a capability impact.
> >
> > Acked-by: Serge Hallyn <serge@hallyn.com>
> >
> > Thanks - looks good to me.
> 
> I don't see a dedicated IPC maintainer/tree, do you want to take this
> via the capabilities tree Serge?

Will do.

-serge

Re: [PATCH] ipc: don't audit capability check in ipc_permissions()

Posted by Alexey Gladkov 2 weeks, 2 days ago

On Thu, Jan 22, 2026 at 03:13:03PM +0100, Ondrej Mosnacek wrote:
> The IPC sysctls implement the ctl_table_root::permissions hook and
> they override the file access mode based on the CAP_CHECKPOINT_RESTORE
> capability, which is being checked regardless of whether any access is
> actually denied or not, so if an LSM denies the capability, an audit
> record may be logged even when access is in fact granted.
> 
> It wouldn't be viable to restructure the sysctl permission logic to only
> check the capability when the access would be actually denied if it's
> not granted. Thus, do the same as in net_ctl_permissions()
> (net/sysctl_net.c) - switch from ns_capable() to ns_capable_noaudit(),
> so that the check never emits an audit record.
> 
> Fixes: 0889f44e2810 ("ipc: Check permissions for checkpoint_restart sysctls at open time")
> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>

Some permission hooks already use ns_capable_noaudit.
For example, pid_table_root_permissions.
I think it makes sense here also.

Acked-by: Alexey Gladkov <legion@kernel.org>

> ---
>  include/linux/capability.h | 6 ++++++
>  ipc/ipc_sysctl.c           | 2 +-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index 1fb08922552c7..37db92b3d6f89 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -203,6 +203,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
>  		ns_capable(ns, CAP_SYS_ADMIN);
>  }
>  
> +static inline bool checkpoint_restore_ns_capable_noaudit(struct user_namespace *ns)
> +{
> +	return ns_capable_noaudit(ns, CAP_CHECKPOINT_RESTORE) ||
> +		ns_capable_noaudit(ns, CAP_SYS_ADMIN);
> +}
> +
>  /* audit system wants to get cap info from files as well */
>  int get_vfs_caps_from_disk(struct mnt_idmap *idmap,
>  			   const struct dentry *dentry,
> diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
> index 15b17e86e198c..9b087ebeb643b 100644
> --- a/ipc/ipc_sysctl.c
> +++ b/ipc/ipc_sysctl.c
> @@ -214,7 +214,7 @@ static int ipc_permissions(struct ctl_table_header *head, const struct ctl_table
>  	if (((table->data == &ns->ids[IPC_SEM_IDS].next_id) ||
>  	     (table->data == &ns->ids[IPC_MSG_IDS].next_id) ||
>  	     (table->data == &ns->ids[IPC_SHM_IDS].next_id)) &&
> -	    checkpoint_restore_ns_capable(ns->user_ns))
> +	    checkpoint_restore_ns_capable_noaudit(ns->user_ns))
>  		mode = 0666;
>  	else
>  #endif
> -- 
> 2.52.0
> 

-- 
Rgrds, legion