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[PATCH v3 07/21] selinux: Add support for unprivileged mounts from user namespaces

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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>
---
 security/selinux/hooks.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 1350167635cb..33beed3ac589 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -820,6 +820,28 @@ 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);
@@ -888,6 +910,7 @@ 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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[PATCH v3 00/21] Support fuse mounts in user namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:40 +0200
  [PATCH v3 17/21] capabilities: Allow privileged user in s_user_ns to set security.* xattrs Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:40 +0200
  [PATCH v3 01/21] fs: fix a posible leak of allocated superblock Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:40 +0200
  [PATCH v3 15/21] fs: Don't remove suid for CAP_FSETID in s_user_ns Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:40 +0200
  [PATCH v3 16/21] fs: Allow superblock owner to access do_remount_sb() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 05/21] block_dev: Check permissions towards block device inode when mounting Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 04/21] block_dev: Support checking inode permissions in lookup_bdev() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 12/21] fs: Refuse uid/gid changes which don't map into s_user_ns Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 14/21] fs: Allow superblock owner to change ownership of inodes with unmappable ids Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
    Re: [PATCH v3 14/21] fs: Allow superblock owner to change ownership  of inodes with unmappable ids "Serge E. Hallyn" <serge@hallyn.com> - 2016-04-25 22:40 +0200
      Re: [PATCH v3 14/21] fs: Allow superblock owner to change ownership  of inodes with unmappable ids Seth Forshee <seth.forshee@canonical.com> - 2016-04-26 21:50 +0200
  [PATCH v3 11/21] cred: Reject inodes with invalid ids in set_create_file_as() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 19/21] fuse: Support fuse filesystems outside of init_user_ns Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 21/21] fuse: Allow user namespace mounts Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 20/21] fuse: Restrict allow_other to the superblock's namespace or a descendant Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 10/21] fs: Check for invalid i_uid in may_follow_link() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 09/21] Smack: Handle labels consistently in untrusted mounts Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 18/21] fuse: Add support for pid namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 08/21] userns: Replace in_userns with current_in_userns Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 06/21] fs: Treat foreign mounts as nosuid Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 18:00 +0200
  [PATCH v3 07/21] selinux: Add support for unprivileged mounts from user namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 18:00 +0200
  [PATCH v3 03/21] fs: Allow sysfs and cgroupfs to share super blocks between user namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 18:00 +0200
    Re: [PATCH v3 03/21] fs: Allow sysfs and cgroupfs to share super  blocks between user namespaces "Serge E. Hallyn" <serge@hallyn.com> - 2016-04-25 21:10 +0200
  [PATCH v3 02/21] fs: Remove check of s_user_ns for existing mounts in fs_fully_visible() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 18:00 +0200

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