diff mbox series

[06/11] ubifs: reorder capability check last

Message ID 20241125104011.36552-5-cgoettsche@seltendoof.de (mailing list archive)
State New
Delegated to: Paul Moore
Headers show
Series [01/11] coccinelle: Add script to reorder capable() calls | expand

Commit Message

Christian Göttsche Nov. 25, 2024, 10:39 a.m. UTC 
From: Christian Göttsche <cgzones@googlemail.com>

capable() calls refer to enabled LSMs whether to permit or deny the
request.  This is relevant in connection with SELinux, where a
capability check results in a policy decision and by default a denial
message on insufficient permission is issued.
It can lead to three undesired cases:
  1. A denial message is generated, even in case the operation was an
     unprivileged one and thus the syscall succeeded, creating noise.
  2. To avoid the noise from 1. the policy writer adds a rule to ignore
     those denial messages, hiding future syscalls, where the task
     performs an actual privileged operation, leading to hidden limited
     functionality of that task.
  3. To avoid the noise from 1. the policy writer adds a rule to permit
     the task the requested capability, while it does not need it,
     violating the principle of least privilege.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
---
 drivers/gpu/drm/panthor/panthor_drv.c | 2 +-
 fs/ubifs/budget.c                     | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

Comments

Liviu Dudau Nov. 25, 2024, 11:10 a.m. UTC | #1 
Hi Christian,

On Mon, Nov 25, 2024 at 11:39:58AM +0100, Christian Göttsche wrote:
> From: Christian Göttsche <cgzones@googlemail.com>
> 
> capable() calls refer to enabled LSMs whether to permit or deny the
> request.  This is relevant in connection with SELinux, where a
> capability check results in a policy decision and by default a denial
> message on insufficient permission is issued.
> It can lead to three undesired cases:
>   1. A denial message is generated, even in case the operation was an
>      unprivileged one and thus the syscall succeeded, creating noise.
>   2. To avoid the noise from 1. the policy writer adds a rule to ignore
>      those denial messages, hiding future syscalls, where the task
>      performs an actual privileged operation, leading to hidden limited
>      functionality of that task.
>   3. To avoid the noise from 1. the policy writer adds a rule to permit
>      the task the requested capability, while it does not need it,
>      violating the principle of least privilege.
> 
> Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
> ---
>  drivers/gpu/drm/panthor/panthor_drv.c | 2 +-
>  fs/ubifs/budget.c                     | 5 +++--
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index ac7e53f6e3f0..2de0c3627fbf 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -791,7 +791,7 @@ static int group_priority_permit(struct drm_file *file,
>  		return 0;
>  
>  	/* Higher priorities require CAP_SYS_NICE or DRM_MASTER */
> -	if (capable(CAP_SYS_NICE) || drm_is_current_master(file))
> +	if (drm_is_current_master(file) || capable(CAP_SYS_NICE))
>  		return 0;
>  
>  	return -EACCES;

Can the patch above be split into a separate one? It's for a different subsystem than ubifs.

Otherwise, it looks good to me, so you can add my Reviewed-by to the new patch.

Best regards,
Liviu

> diff --git a/fs/ubifs/budget.c b/fs/ubifs/budget.c
> index d76eb7b39f56..6137aeadec3f 100644
> --- a/fs/ubifs/budget.c
> +++ b/fs/ubifs/budget.c
> @@ -256,8 +256,9 @@ long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
>   */
>  static int can_use_rp(struct ubifs_info *c)
>  {
> -	if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
> -	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
> +	if (uid_eq(current_fsuid(), c->rp_uid) ||
> +	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)) ||
> +	    capable(CAP_SYS_RESOURCE))
>  		return 1;
>  	return 0;
>  }
> -- 
> 2.45.2
>
Richard Weinberger Nov. 25, 2024, 11:30 a.m. UTC | #2 
----- Ursprüngliche Mail -----
> Von: "Christian Göttsche" <cgoettsche@seltendoof.de>
> capable() calls refer to enabled LSMs whether to permit or deny the
> request.  This is relevant in connection with SELinux, where a
> capability check results in a policy decision and by default a denial
> message on insufficient permission is issued.
> It can lead to three undesired cases:
>  1. A denial message is generated, even in case the operation was an
>     unprivileged one and thus the syscall succeeded, creating noise.
>  2. To avoid the noise from 1. the policy writer adds a rule to ignore
>     those denial messages, hiding future syscalls, where the task
>     performs an actual privileged operation, leading to hidden limited
>     functionality of that task.
>  3. To avoid the noise from 1. the policy writer adds a rule to permit
>     the task the requested capability, while it does not need it,
>     violating the principle of least privilege.
> 
> Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
> ---
> drivers/gpu/drm/panthor/panthor_drv.c | 2 +-

This change is unrelated, please remove it.

> fs/ubifs/budget.c                     | 5 +++--
> 2 files changed, 4 insertions(+), 3 deletions(-)

[...]

> diff --git a/fs/ubifs/budget.c b/fs/ubifs/budget.c
> index d76eb7b39f56..6137aeadec3f 100644
> --- a/fs/ubifs/budget.c
> +++ b/fs/ubifs/budget.c
> @@ -256,8 +256,9 @@ long long ubifs_calc_available(const struct ubifs_info *c,
> int min_idx_lebs)
>  */
> static int can_use_rp(struct ubifs_info *c)
> {
> -	if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
> -	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
> +	if (uid_eq(current_fsuid(), c->rp_uid) ||
> +	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)) ||
> +	    capable(CAP_SYS_RESOURCE))
> 		return 1;
> 	return 0;
> }

The UBIFS part looks ok:

Acked-by: Richard Weinberger <richard@nod.at>

Since I was not CC'ed to the whole series, I miss a lot of context.
Will this series merged as a whole? By whom?

Thanks,
//richard
Christian Göttsche Nov. 25, 2024, 11:48 a.m. UTC | #3 
On Mon, 25 Nov 2024 at 12:31, Richard Weinberger <richard@nod.at> wrote:
>
> ----- Ursprüngliche Mail -----
> > Von: "Christian Göttsche" <cgoettsche@seltendoof.de>
> > capable() calls refer to enabled LSMs whether to permit or deny the
> > request.  This is relevant in connection with SELinux, where a
> > capability check results in a policy decision and by default a denial
> > message on insufficient permission is issued.
> > It can lead to three undesired cases:
> >  1. A denial message is generated, even in case the operation was an
> >     unprivileged one and thus the syscall succeeded, creating noise.
> >  2. To avoid the noise from 1. the policy writer adds a rule to ignore
> >     those denial messages, hiding future syscalls, where the task
> >     performs an actual privileged operation, leading to hidden limited
> >     functionality of that task.
> >  3. To avoid the noise from 1. the policy writer adds a rule to permit
> >     the task the requested capability, while it does not need it,
> >     violating the principle of least privilege.
> >
> > Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
> > ---
> > drivers/gpu/drm/panthor/panthor_drv.c | 2 +-
>
> This change is unrelated, please remove it.

Sorry, somehow these two changes got erroneously combined in a single patch.
I'll send a v2 with them split into separate ones.

>
> > fs/ubifs/budget.c                     | 5 +++--
> > 2 files changed, 4 insertions(+), 3 deletions(-)
>
> [...]
>
> > diff --git a/fs/ubifs/budget.c b/fs/ubifs/budget.c
> > index d76eb7b39f56..6137aeadec3f 100644
> > --- a/fs/ubifs/budget.c
> > +++ b/fs/ubifs/budget.c
> > @@ -256,8 +256,9 @@ long long ubifs_calc_available(const struct ubifs_info *c,
> > int min_idx_lebs)
> >  */
> > static int can_use_rp(struct ubifs_info *c)
> > {
> > -     if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
> > -         (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
> > +     if (uid_eq(current_fsuid(), c->rp_uid) ||
> > +         (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)) ||
> > +         capable(CAP_SYS_RESOURCE))
> >               return 1;
> >       return 0;
> > }
>
> The UBIFS part looks ok:
>
> Acked-by: Richard Weinberger <richard@nod.at>
>
> Since I was not CC'ed to the whole series, I miss a lot of context.

The series consists of similar patches to other subsystems and a
coccinelle script addition.
See https://lore.kernel.org/linux-security-module/20241125104011.36552-11-cgoettsche@seltendoof.de/#t

> Will this series merged as a whole? By whom?
>
> Thanks,
> //richard
diff mbox series

Patch

diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
index ac7e53f6e3f0..2de0c3627fbf 100644
--- a/drivers/gpu/drm/panthor/panthor_drv.c
+++ b/drivers/gpu/drm/panthor/panthor_drv.c
@@ -791,7 +791,7 @@  static int group_priority_permit(struct drm_file *file,
 		return 0;
 
 	/* Higher priorities require CAP_SYS_NICE or DRM_MASTER */
-	if (capable(CAP_SYS_NICE) || drm_is_current_master(file))
+	if (drm_is_current_master(file) || capable(CAP_SYS_NICE))
 		return 0;
 
 	return -EACCES;
diff --git a/fs/ubifs/budget.c b/fs/ubifs/budget.c
index d76eb7b39f56..6137aeadec3f 100644
--- a/fs/ubifs/budget.c
+++ b/fs/ubifs/budget.c
@@ -256,8 +256,9 @@  long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
  */
 static int can_use_rp(struct ubifs_info *c)
 {
-	if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
-	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
+	if (uid_eq(current_fsuid(), c->rp_uid) ||
+	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)) ||
+	    capable(CAP_SYS_RESOURCE))
 		return 1;
 	return 0;
 }