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[PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

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  [PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant Seth Forshee <seth.forshee@canonical.com> - 2015-12-02 16:50 +0100
    Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's  namespace or a descendant "Serge E. Hallyn" <serge@hallyn.com> - 2015-12-04 21:10 +0100
      Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's  namespace or a descendant Seth Forshee <seth.forshee@canonical.com> - 2015-12-04 21:50 +0100
        Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's  namespace or a descendant "Serge E. Hallyn" <serge.hallyn@ubuntu.com> - 2015-12-04 23:00 +0100

#1281937 — [PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

Unprivileged users are normally restricted from mounting with the
allow_other option by system policy, but this could be bypassed
for a mount done with user namespace root permissions. In such
cases allow_other should not allow users outside the userns
to access the mount as doing so would give the unprivileged user
the ability to manipulate processes it would otherwise be unable
to manipulate. Restrict allow_other to apply to users in the same
userns used at mount or a descendant of that namespace.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/fuse/dir.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index f67f4dd86b36..5b8edb1203b8 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1018,8 +1018,14 @@ int fuse_allow_current_process(struct fuse_conn *fc)
 {
 	const struct cred *cred;
 
-	if (fc->flags & FUSE_ALLOW_OTHER)
-		return 1;
+	if (fc->flags & FUSE_ALLOW_OTHER) {
+		struct user_namespace *ns;
+		for (ns = current_user_ns(); ns; ns = ns->parent) {
+			if (ns == fc->user_ns)
+				return 1;
+		}
+		return 0;
+	}
 
 	cred = current_cred();
 	if (uid_eq(cred->euid, fc->user_id) &&
-- 
1.9.1

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#1284190 — Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

Quoting Seth Forshee (seth.forshee@canonical.com):
> Unprivileged users are normally restricted from mounting with the
> allow_other option by system policy, but this could be bypassed
> for a mount done with user namespace root permissions. In such
> cases allow_other should not allow users outside the userns
> to access the mount as doing so would give the unprivileged user
> the ability to manipulate processes it would otherwise be unable
> to manipulate. Restrict allow_other to apply to users in the same
> userns used at mount or a descendant of that namespace.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> ---
>  fs/fuse/dir.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index f67f4dd86b36..5b8edb1203b8 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -1018,8 +1018,14 @@ int fuse_allow_current_process(struct fuse_conn *fc)
>  {
>  	const struct cred *cred;
>  
> -	if (fc->flags & FUSE_ALLOW_OTHER)
> -		return 1;
> +	if (fc->flags & FUSE_ALLOW_OTHER) {
> +		struct user_namespace *ns;
> +		for (ns = current_user_ns(); ns; ns = ns->parent) {
> +			if (ns == fc->user_ns)
> +				return 1;
> +		}

	use current_in_userns() ?

> +		return 0;
> +	}
>  
>  	cred = current_cred();
>  	if (uid_eq(cred->euid, fc->user_id) &&
> -- 
> 1.9.1
> 
> --
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#1284220 — Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

On Fri, Dec 04, 2015 at 02:05:41PM -0600, Serge E. Hallyn wrote:
> Quoting Seth Forshee (seth.forshee@canonical.com):
> > Unprivileged users are normally restricted from mounting with the
> > allow_other option by system policy, but this could be bypassed
> > for a mount done with user namespace root permissions. In such
> > cases allow_other should not allow users outside the userns
> > to access the mount as doing so would give the unprivileged user
> > the ability to manipulate processes it would otherwise be unable
> > to manipulate. Restrict allow_other to apply to users in the same
> > userns used at mount or a descendant of that namespace.
> > 
> > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > ---
> >  fs/fuse/dir.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> > index f67f4dd86b36..5b8edb1203b8 100644
> > --- a/fs/fuse/dir.c
> > +++ b/fs/fuse/dir.c
> > @@ -1018,8 +1018,14 @@ int fuse_allow_current_process(struct fuse_conn *fc)
> >  {
> >  	const struct cred *cred;
> >  
> > -	if (fc->flags & FUSE_ALLOW_OTHER)
> > -		return 1;
> > +	if (fc->flags & FUSE_ALLOW_OTHER) {
> > +		struct user_namespace *ns;
> > +		for (ns = current_user_ns(); ns; ns = ns->parent) {
> > +			if (ns == fc->user_ns)
> > +				return 1;
> > +		}
> 
> 	use current_in_userns() ?

Yes, it should. I wrote this before I wrote the patch which adds that
function and never thought to go back to change it here.
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#1284266 — Re: [PATCH 18/19] fuse: Restrict allow_other to the superblock's namespace or a descendant

On Fri, Dec 04, 2015 at 02:43:19PM -0600, Seth Forshee wrote:
> On Fri, Dec 04, 2015 at 02:05:41PM -0600, Serge E. Hallyn wrote:
> > Quoting Seth Forshee (seth.forshee@canonical.com):
> > > Unprivileged users are normally restricted from mounting with the
> > > allow_other option by system policy, but this could be bypassed
> > > for a mount done with user namespace root permissions. In such
> > > cases allow_other should not allow users outside the userns
> > > to access the mount as doing so would give the unprivileged user
> > > the ability to manipulate processes it would otherwise be unable
> > > to manipulate. Restrict allow_other to apply to users in the same
> > > userns used at mount or a descendant of that namespace.
> > > 
> > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > > ---
> > >  fs/fuse/dir.c | 10 ++++++++--
> > >  1 file changed, 8 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> > > index f67f4dd86b36..5b8edb1203b8 100644
> > > --- a/fs/fuse/dir.c
> > > +++ b/fs/fuse/dir.c
> > > @@ -1018,8 +1018,14 @@ int fuse_allow_current_process(struct fuse_conn *fc)
> > >  {
> > >  	const struct cred *cred;
> > >  
> > > -	if (fc->flags & FUSE_ALLOW_OTHER)
> > > -		return 1;
> > > +	if (fc->flags & FUSE_ALLOW_OTHER) {
> > > +		struct user_namespace *ns;
> > > +		for (ns = current_user_ns(); ns; ns = ns->parent) {
> > > +			if (ns == fc->user_ns)
> > > +				return 1;
> > > +		}
> > 
> > 	use current_in_userns() ?
> 
> Yes, it should. I wrote this before I wrote the patch which adds that
> function and never thought to go back to change it here.

Ok - 

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

thanks.
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