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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Stephen Smalley <sds@tycho.nsa.gov>,
        Ondrej Mosnacek <omosnace@redhat.com>,
        Paul Moore <paul@paul-moore.com>
Subject: [PATCH 5.4 86/96] selinux: fix regression introduced by move_mount(2) syscall
Date:   Thu, 13 Feb 2020 07:21:33 -0800
Message-Id: <20200213151911.459785249@linuxfoundation.org>
In-Reply-To: <20200213151839.156309910@linuxfoundation.org>
References: <20200213151839.156309910@linuxfoundation.org>
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From: Stephen Smalley <sds@tycho.nsa.gov>

commit 98aa00345de54b8340dc2ddcd87f446d33387b5e upstream.

commit 2db154b3ea8e ("vfs: syscall: Add move_mount(2) to move mounts around")
introduced a new move_mount(2) system call and a corresponding new LSM
security_move_mount hook but did not implement this hook for any existing
LSM.  This creates a regression for SELinux with respect to consistent
checking of mounts; the existing selinux_mount hook checks mounton
permission to the mount point path.  Provide a SELinux hook
implementation for move_mount that applies this same check for
consistency.  In the future we may wish to add a new move_mount
filesystem permission and check as well, but this addresses
the immediate regression.

Fixes: 2db154b3ea8e ("vfs: syscall: Add move_mount(2) to move mounts around")
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Reviewed-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 security/selinux/hooks.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2766,6 +2766,14 @@ static int selinux_mount(const char *dev
 		return path_has_perm(cred, path, FILE__MOUNTON);
 }
 
+static int selinux_move_mount(const struct path *from_path,
+			      const struct path *to_path)
+{
+	const struct cred *cred = current_cred();
+
+	return path_has_perm(cred, to_path, FILE__MOUNTON);
+}
+
 static int selinux_umount(struct vfsmount *mnt, int flags)
 {
 	const struct cred *cred = current_cred();
@@ -6835,6 +6843,8 @@ static struct security_hook_list selinux
 	LSM_HOOK_INIT(sb_clone_mnt_opts, selinux_sb_clone_mnt_opts),
 	LSM_HOOK_INIT(sb_add_mnt_opt, selinux_add_mnt_opt),
 
+	LSM_HOOK_INIT(move_mount, selinux_move_mount),
+
 	LSM_HOOK_INIT(dentry_init_security, selinux_dentry_init_security),
 	LSM_HOOK_INIT(dentry_create_files_as, selinux_dentry_create_files_as),