From: Jonathan Lebon jlebon@redhat.com
mainline inclusion from mainline-v5.5-rc1 commit 3e3e24b42043eceb97ed834102c2d094dfd7aaa6 category: bugfix
---------------------------
Currently, the SELinux LSM prevents one from setting the `security.selinux` xattr on an inode without a policy first being loaded. However, this restriction is problematic: it makes it impossible to have newly created files with the correct label before actually loading the policy.
This is relevant in distributions like Fedora, where the policy is loaded by systemd shortly after pivoting out of the initrd. In such instances, all files created prior to pivoting will be unlabeled. One then has to relabel them after pivoting, an operation which inherently races with other processes trying to access those same files.
Going further, there are use cases for creating the entire root filesystem on first boot from the initrd (e.g. Container Linux supports this today[1], and we'd like to support it in Fedora CoreOS as well[2]). One can imagine doing this in two ways: at the block device level (e.g. laying down a disk image), or at the filesystem level. In the former, labeling can simply be part of the image. But even in the latter scenario, one still really wants to be able to set the right labels when populating the new filesystem.
This patch enables this by changing behaviour in the following two ways: 1. allow `setxattr` on mounts without `SBLABEL_MNT` (which is all of them if no policy is loaded yet) 2. don't try to set the in-core inode SID if we're not initialized; instead leave it as `LABEL_INVALID` so that revalidation may be attempted at a later time
Note the first hunk of this patch is functionally the same as a previously discussed one[3], though it was part of a larger series which wasn't accepted.
Co-developed-by: Victor Kamensky kamensky@cisco.com Signed-off-by: Victor Kamensky kamensky@cisco.com Signed-off-by: Jonathan Lebon jlebon@redhat.com
[1] https://coreos.com/os/docs/latest/root-filesystem-placement.html [2] https://github.com/coreos/fedora-coreos-tracker/issues/94 [3] https://www.spinics.net/lists/linux-initramfs/msg04593.html --- security/selinux/hooks.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 452254fd89f8..931546d80211 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -3305,7 +3305,7 @@ static int selinux_inode_setxattr(struct dentry *dentry, const char *name, }
sbsec = inode->i_sb->s_security; - if (!(sbsec->flags & SBLABEL_MNT)) + if (!(sbsec->flags & SBLABEL_MNT) && selinux_state.initialized) return -EOPNOTSUPP;
if (!inode_owner_or_capable(inode)) @@ -3387,6 +3387,15 @@ static void selinux_inode_post_setxattr(struct dentry *dentry, const char *name, return; }
+ if (!selinux_state.initialized) { + /* If we haven't even been initialized, then we can't validate + * against a policy, so leave the label as invalid. It may + * resolve to a valid label on the next revalidation try if + * we've since initialized. + */ + return; + } + rc = security_context_to_sid_force(&selinux_state, value, size, &newsid); if (rc) {