On Thu, Sep 29, 2022 at 03:15:17PM -0400, Paul Moore wrote: > 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. Done.
