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[PATCH v3 5/7] selinux: Add support for unprivileged mounts from user namespaces

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  [PATCH v3 5/7] selinux: Add support for unprivileged mounts from user namespaces Seth Forshee <seth.forshee@canonical.com> - 2015-11-17 17:50 +0100
    Re: [PATCH v3 5/7] selinux: Add support for unprivileged mounts from  user namespaces James Morris <jmorris@namei.org> - 2015-11-18 01:10 +0100

#1271410 — [PATCH v3 5/7] selinux: Add support for unprivileged mounts from user namespaces

Security labels from unprivileged mounts in user namespaces must
be ignored. Force superblocks from user namespaces whose labeling
behavior is to use xattrs to use mountpoint labeling instead.
For the mountpoint label, default to converting the current task
context into a form suitable for file objects, but also allow the
policy writer to specify a different label through policy
transition rules.

Pieced together from code snippets provided by Stephen Smalley.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
---
 security/selinux/hooks.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index de05207eb665..09be1dc21e58 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -756,6 +756,28 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 			goto out;
 		}
 	}
+
+	/*
+	 * If this is a user namespace mount, no contexts are allowed
+	 * on the command line and security labels must be ignored.
+	 */
+	if (sb->s_user_ns != &init_user_ns) {
+		if (context_sid || fscontext_sid || rootcontext_sid ||
+		    defcontext_sid) {
+			rc = -EACCES;
+			goto out;
+		}
+		if (sbsec->behavior == SECURITY_FS_USE_XATTR) {
+			sbsec->behavior = SECURITY_FS_USE_MNTPOINT;
+			rc = security_transition_sid(current_sid(), current_sid(),
+						     SECCLASS_FILE, NULL,
+						     &sbsec->mntpoint_sid);
+			if (rc)
+				goto out;
+		}
+		goto out_set_opts;
+	}
+
 	/* sets the context of the superblock for the fs being mounted. */
 	if (fscontext_sid) {
 		rc = may_context_mount_sb_relabel(fscontext_sid, sbsec, cred);
@@ -824,6 +846,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 		sbsec->def_sid = defcontext_sid;
 	}
 
+out_set_opts:
 	rc = sb_finish_set_opts(sb);
 out:
 	mutex_unlock(&sbsec->lock);
-- 
1.9.1

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#1271752 — Re: [PATCH v3 5/7] selinux: Add support for unprivileged mounts from user namespaces

On Tue, 17 Nov 2015, Seth Forshee wrote:

> Security labels from unprivileged mounts in user namespaces must
> be ignored. Force superblocks from user namespaces whose labeling
> behavior is to use xattrs to use mountpoint labeling instead.
> For the mountpoint label, default to converting the current task
> context into a form suitable for file objects, but also allow the
> policy writer to specify a different label through policy
> transition rules.
> 
> Pieced together from code snippets provided by Stephen Smalley.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> Acked-by: Stephen Smalley <sds@tycho.nsa.gov>


Acked-by: James Morris <james.l.morris@oracle.com>

-- 
James Morris
<jmorris@namei.org>

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