On 9/26/2022 7:08 AM, Christian Brauner 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. Smack 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 > this all becomes a very simple hook for smack. > > Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@xxxxxxxxxx [1] > Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx> The Smack hook looks fine. Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx> > --- > > Notes: > /* v2 */ > unchanged > > security/smack/smack_lsm.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c > index 001831458fa2..ec6d55632b4f 100644 > --- a/security/smack/smack_lsm.c > +++ b/security/smack/smack_lsm.c > @@ -1393,6 +1393,29 @@ static int smack_inode_removexattr(struct user_namespace *mnt_userns, > return 0; > } > > +/** > + * smack_inode_set_acl - Smack check for setting posix acls > + * @mnt_userns: the userns attached to the mnt this request came from > + * @dentry: the object > + * @acl_name: name of the posix acl > + * @kacl: the posix acls > + * > + * Returns 0 if access is permitted, an error code otherwise > + */ > +static int smack_inode_set_acl(struct user_namespace *mnt_userns, > + struct dentry *dentry, const char *acl_name, > + struct posix_acl *kacl) > +{ > + struct smk_audit_info ad; > + int rc; > + > + smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_DENTRY); > + smk_ad_setfield_u_fs_path_dentry(&ad, dentry); > + rc = smk_curacc(smk_of_inode(d_backing_inode(dentry)), MAY_WRITE, &ad); > + rc = smk_bu_inode(d_backing_inode(dentry), MAY_WRITE, rc); > + return rc; > +} > + > /** > * smack_inode_getsecurity - get smack xattrs > * @mnt_userns: active user namespace > @@ -4772,6 +4795,7 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = { > LSM_HOOK_INIT(inode_post_setxattr, smack_inode_post_setxattr), > LSM_HOOK_INIT(inode_getxattr, smack_inode_getxattr), > LSM_HOOK_INIT(inode_removexattr, smack_inode_removexattr), > + LSM_HOOK_INIT(inode_set_acl, smack_inode_set_acl), > LSM_HOOK_INIT(inode_getsecurity, smack_inode_getsecurity), > LSM_HOOK_INIT(inode_setsecurity, smack_inode_setsecurity), > LSM_HOOK_INIT(inode_listsecurity, smack_inode_listsecurity),
