The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5881fa8dc2de9697a89451f6518e8b3a796c09c6 Mon Sep 17 00:00:00 2001

From: Ondrej Mosnacek omosnace@redhat.com Date: Fri, 7 May 2021 14:53:04 +0200 Subject: [PATCH] debugfs: fix security_locked_down() call for SELinux

When (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) is zero, then the SELinux implementation of the locked_down hook might report a denial even though the operation would actually be allowed.

To fix this, make sure that security_locked_down() is called only when the return value will be taken into account (i.e. when changing one of the problematic attributes).

Note: this was introduced by commit 5496197f9b08 ("debugfs: Restrict debugfs when the kernel is locked down"), but it didn't matter at that time, as the SELinux support came in later.

Fixes: 59438b46471a ("security,lockdown,selinux: implement SELinux lockdown") Cc: stable stable@vger.kernel.org Signed-off-by: Ondrej Mosnacek omosnace@redhat.com Link: https://lore.kernel.org/r/20210507125304.144394-1-omosnace@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c index 1d252164d97b..8129a430d789 100644 --- a/fs/debugfs/inode.c +++ b/fs/debugfs/inode.c @@ -45,10 +45,13 @@ static unsigned int debugfs_allow __ro_after_init = DEFAULT_DEBUGFS_ALLOW_BITS; static int debugfs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry, struct iattr *ia) { - int ret = security_locked_down(LOCKDOWN_DEBUGFS); + int ret;

- if (ret && (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))) - return ret; + if (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) { + ret = security_locked_down(LOCKDOWN_DEBUGFS); + if (ret) + return ret; + } return simple_setattr(&init_user_ns, dentry, ia); }