On Wed, Sep 28, 2022 at 10:58:33AM -0400, Paul Moore wrote: > On Wed, Sep 28, 2022 at 3:40 AM Christian Brauner <brauner@xxxxxxxxxx> wrote: > > > > On Tue, Sep 27, 2022 at 06:55:25PM -0400, Paul Moore wrote: > > > On Mon, Sep 26, 2022 at 11:24 AM Christian Brauner <brauner@xxxxxxxxxx> wrote: > > > > > > > > In previous patches we implemented get and set inode operations for all > > > > non-stacking filesystems that support posix acls but didn't yet > > > > implement get and/or set acl inode operations. This specifically > > > > affected cifs and 9p. > > > > > > > > Now we can build a posix acl api based solely on get and set inode > > > > operations. We add a new vfs_get_acl() api that can be used to get posix > > > > acls. This finally removes all type unsafety and type conversion issues > > > > explained in detail in [1] that we aim to get rid of. > > > > > > > > After we finished building the vfs api we can switch stacking > > > > filesystems to rely on the new posix api and then finally switch the > > > > xattr system calls themselves to rely on the posix acl api. > > > > > > > > Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@xxxxxxxxxx [1] > > > > Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx> > > > > --- > > > > > > > > Notes: > > > > /* v2 */ > > > > unchanged > > > > > > > > fs/posix_acl.c | 131 ++++++++++++++++++++++++++++++-- > > > > include/linux/posix_acl.h | 9 +++ > > > > include/linux/posix_acl_xattr.h | 10 +++ > > > > 3 files changed, 142 insertions(+), 8 deletions(-) > > > > > > ... > > > > > > > diff --git a/fs/posix_acl.c b/fs/posix_acl.c > > > > index ef0908a4bc46..18873be583a9 100644 > > > > --- a/fs/posix_acl.c > > > > +++ b/fs/posix_acl.c > > > > @@ -1369,3 +1439,48 @@ int vfs_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry, > > > > return error; > > > > } > > > > EXPORT_SYMBOL(vfs_set_acl); > > > > + > > > > +/** > > > > + * vfs_get_acl - get posix acls > > > > + * @mnt_userns: user namespace of the mount > > > > + * @dentry: the dentry based on which to retrieve the posix acls > > > > + * @acl_name: the name of the posix acl > > > > + * > > > > + * This function retrieves @kacl from the filesystem. The caller must all > > > > + * posix_acl_release() on @kacl. > > > > + * > > > > + * Return: On success POSIX ACLs in VFS format, on error negative errno. > > > > + */ > > > > +struct posix_acl *vfs_get_acl(struct user_namespace *mnt_userns, > > > > + struct dentry *dentry, const char *acl_name) > > > > +{ > > > > + struct inode *inode = d_inode(dentry); > > > > + struct posix_acl *acl; > > > > + int acl_type, error; > > > > + > > > > + acl_type = posix_acl_type(acl_name); > > > > + if (acl_type < 0) > > > > + return ERR_PTR(-EINVAL); > > > > + > > > > + /* > > > > + * The VFS has no restrictions on reading POSIX ACLs so calling > > > > + * something like xattr_permission() isn't needed. Only LSMs get a say. > > > > + */ > > > > + error = security_inode_getxattr(dentry, acl_name); > > > > + if (error) > > > > + return ERR_PTR(error); > > > > > > I understand the desire to reuse the security_inode_getxattr() hook > > > here, it makes perfect sense, but given that this patchset introduces > > > an ACL specific setter hook I think it makes sense to have a matching > > > getter hook. It's arguably a little silly given the current crop of > > > LSMs and their approach to ACLs, but if we are going to differentiate > > > on the write side I think we might as well be consistent and > > > differentiate on the read side as well. > > > > Sure, I don't mind doing that. I'll add the infrastructure and then the > > individual LSMs can add their own hooks. > > Adding the ACL hook infrastructure, including the call in > vfs_get_acl(), without the LSM implementations would result in an > access control regression for both SELinux and Smack. Similar issues > with the removexattr hook, although that looks to have IMA/EVM calls > too (which may be noops in the case of an ACL, I haven't checked). > > The good news is that the individual LSM implementations should be > trivial, and if you wanted to just have the new ACL hook > implementations call into the existing xattr implementations inside > each LSM I think that would be okay to start. Yeah, I realized right after I sent the mail that I'd need to implement them. I think I came up with something fairly minimal for all lsms and the integrity modules. I folded the trivial patches for adding get, set, and remove hooks for the individual modules together to not needlessly inflate the security portion of the patchset.
