6.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ondrej Mosnacek <omosnace@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx> Reported-by: Adam Williamson <awilliam@xxxxxxxxxx> 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@xxxxxxxxxx> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx> Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- security/selinux/hooks.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2748,14 +2748,20 @@ static int selinux_umount(struct vfsmoun 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)
