From 978b86fbdb2acf69a3630931f0c4f07a30734f2f Mon Sep 17 00:00:00 2001
From: Ondrej Mosnacek <omosnace@redhat.com>
Date: Mon, 11 Sep 2023 16:23:58 +0200
Subject: [PATCH] selinux: fix handling of empty opts in
selinux_fs_context_submount()
commit ccf1dab96be4caed7c5235b1cfdb606ac161b996 upstream.
selinux_set_mnt_opts() relies on the fact that the mount options pointer
is always NULL when all options are unset (specifically in its
!selinux_initialized() branch. However, the new
selinux_fs_context_submount() hook breaks this rule by allocating a new
structure even if no options are set. That causes any submount created
before a SELinux policy is loaded to be rejected in
selinux_set_mnt_opts().
Fix this by making selinux_fs_context_submount() leave fc->security
set to NULL when there are no options to be copied from the reference
superblock.
Cc: <stable@vger.kernel.org>
Reported-by: Adam Williamson <awilliam@redhat.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2236345
Fixes: d80a8f1b58c2 ("vfs, security: Fix automount superblock LSM init problem, preventing NFS sb sharing")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
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, 8 insertions(+), 2 deletions(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 26c9e4da4efc..d88c399b0e86 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2769,14 +2769,20 @@ static int selinux_umount(struct vfsmount *mnt, int flags)
static int selinux_fs_context_submount(struct fs_context *fc,
struct super_block *reference)
{
- const struct superblock_security_struct *sbsec;
+ const struct superblock_security_struct *sbsec = selinux_superblock(reference);
struct selinux_mnt_opts *opts;
+ /*
+ * Ensure that fc->security remains NULL when no options are set
+ * as expected by selinux_set_mnt_opts().
+ */
+ if (!(sbsec->flags & (FSCONTEXT_MNT|CONTEXT_MNT|DEFCONTEXT_MNT)))
+ return 0;
+
opts = kzalloc(sizeof(*opts), GFP_KERNEL);
if (!opts)
return -ENOMEM;
- sbsec = selinux_superblock(reference);
if (sbsec->flags & FSCONTEXT_MNT)
opts->fscontext_sid = sbsec->sid;
if (sbsec->flags & CONTEXT_MNT)