On Thu, Sep 29, 2022 at 11:31 AM Christian Brauner <brauner@xxxxxxxxxx> wrote: > > The current way of setting and getting posix acls through the generic > xattr interface is error prone and type unsafe. The vfs needs to > interpret and fixup posix acls before storing or reporting it to > userspace. Various hacks exist to make this work. The code is hard to > understand and difficult to maintain in it's current form. Instead of > making this work by hacking posix acls through xattr handlers we are > building a dedicated posix acl api around the get and set inode > operations. This removes a lot of hackiness and makes the codepaths > easier to maintain. A lot of background can be found in [1]. > > So far posix acls were passed as a void blob to the security and > integrity modules. Some of them like evm then proceed to interpret the > void pointer and convert it into the kernel internal struct posix acl > representation to perform their integrity checking magic. This is > obviously pretty problematic as that requires knowledge that only the > vfs is guaranteed to have and has lead to various bugs. Add a proper > security hook for setting posix acls and pass down the posix acls in > their appropriate vfs format instead of hacking it through a void > pointer stored in the uapi format. > > I spent considerate time in the security module infrastructure and > audited all codepaths. SELinux has no restrictions based on the posix > acl values passed through it. The capability hook doesn't need to be > called either because it only has restrictions on security.* xattrs. So > these are all fairly simply hooks for SELinux. > > Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@xxxxxxxxxx [1] > Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx> > --- > > Notes: > /* v2 */ > unchanged > > /* v3 */ > Paul Moore <paul@xxxxxxxxxxxxxx>: > - Add get, and remove acl hook > > /* v4 */ > unchanged > > security/selinux/hooks.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) One small nitpick below, but looks good regardless. Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index 79573504783b..0e3cd67e5e92 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -3239,6 +3239,27 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns, > &ad); > } > > +static int selinux_inode_set_acl(struct user_namespace *mnt_userns, > + struct dentry *dentry, const char *acl_name, > + struct posix_acl *kacl) > +{ > + return dentry_has_perm(current_cred(), dentry, FILE__SETATTR); > +} > + > +static int selinux_inode_get_acl(struct user_namespace *mnt_userns, > + struct dentry *dentry, const char *acl_name) > +{ > + const struct cred *cred = current_cred(); > + > + return dentry_has_perm(cred, dentry, FILE__GETATTR); > +} Both the set and remove hooks use current_cred() directly in the call to dentry_has_perm(), you might as well do the same in the get hook. > +static int selinux_inode_remove_acl(struct user_namespace *mnt_userns, > + struct dentry *dentry, const char *acl_name) > +{ > + return dentry_has_perm(current_cred(), dentry, FILE__SETATTR); > +} -- paul-moore.com
