Re: [PATCH v23 09/22] richacl: Permission check algorithm

Jeff Layton
2016-07-05T14:59:12Z

On Thu, 2016-06-30 at 15:47 +0200, Andreas Gruenbacher wrote:
> A richacl roughly grants a requested access if the NFSv4 acl in the
> richacl grants the requested permissions according to the NFSv4
> permission check algorithm and the file mask that applies to the process
> includes the requested permissions.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> Reviewed-by: J. Bruce Fields <bfields@fieldses.org>
> ---
>  fs/richacl.c            | 128 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/richacl.h |   1 +
>  2 files changed, 129 insertions(+)
>
> diff --git a/fs/richacl.c b/fs/richacl.c
> index 056228f..cb0ef3f 100644
> --- a/fs/richacl.c
> +++ b/fs/richacl.c
> @@ -338,3 +338,131 @@ restart:
>   acl->a_flags &= ~(RICHACL_WRITE_THROUGH | RICHACL_MASKED);
>  }
>  EXPORT_SYMBOL_GPL(richacl_compute_max_masks);
> +
> +/**
> + * richacl_permission  -  richacl permission check algorithm
> + * @inode: inode to check
> + * @acl: rich acl of the inode
> + * @want: requested access (MAY_* flags)
> + *
> + * Checks if the current process is granted @mask flags in @acl.
> + */

nit: there is no @mask parm here. Do you mean @want ?

> +int
> +richacl_permission(struct inode *inode, const struct richacl *acl,
> +    int want)
> +{
> + const struct richace *ace;
> + unsigned int mask = richacl_want_to_mask(want);
> + unsigned int requested = mask, denied = 0;
> + int in_owning_group = in_group_p(inode->i_gid);
> + int in_owner_or_group_class = in_owning_group;
> +
> + /*
> +  * A process is
> +  *   - in the owner file class if it owns the file,
> +  *   - in the group file class if it is in the file's owning group or
> +  *     it matches any of the user or group entries, and
> +  *   - in the other file class otherwise.
> +  * The file class is only relevant for determining which file mask to
> +  * apply, which only happens for masked acls.
> +  */
> + if (acl->a_flags & RICHACL_MASKED) {
> + if ((acl->a_flags & RICHACL_WRITE_THROUGH) &&
> +     uid_eq(current_fsuid(), inode->i_uid)) {
> + denied = requested & ~acl->a_owner_mask;
> + goto out;
> + }
> + } else {
> + /*
> +  * When the acl is not masked, there is no need to determine if
> +  * the process is in the group class and we can break out
> +  * earlier of the loop below.
> +  */
> + in_owner_or_group_class = 1;
> + }
> +
> + /*
> +  * Check if the acl grants the requested access and determine which
> +  * file class the process is in.
> +  */
> + richacl_for_each_entry(ace, acl) {
> + unsigned int ace_mask = ace->e_mask;
> +
> + if (richace_is_inherit_only(ace))
> + continue;
> + if (richace_is_owner(ace)) {
> + if (!uid_eq(current_fsuid(), inode->i_uid))
> + continue;
> + goto entry_matches_owner;
> + } else if (richace_is_group(ace)) {
> + if (!in_owning_group)
> + continue;
> + } else if (richace_is_unix_user(ace)) {
> + if (!uid_eq(current_fsuid(), ace->e_id.uid))
> + continue;
> + if (uid_eq(current_fsuid(), inode->i_uid))
> + goto entry_matches_owner;
> + } else if (richace_is_unix_group(ace)) {
> + if (!in_group_p(ace->e_id.gid))
> + continue;
> + } else
> + goto entry_matches_everyone;
> +
> + /*
> +  * Apply the group file mask to entries other than owner@ and
> +  * everyone@ or user entries matching the owner.  This ensures
> +  * that we grant the same permissions as the acl computed by
> +  * richacl_apply_masks().
> +  *
> +  * Without this restriction, the following richacl would grant
> +  * rw access to processes which are both the owner and in the
> +  * owning group, but not to other users in the owning group,
> +  * which could not be represented without masks:
> +  *
> +  *  owner:rw::mask
> +  *  group@:rw::allow
> +  */
> + if ((acl->a_flags & RICHACL_MASKED) && richace_is_allow(ace))
> + ace_mask &= acl->a_group_mask;
> +
> +entry_matches_owner:
> + /* The process is in the owner or group file class. */
> + in_owner_or_group_class = 1;
> +
> +entry_matches_everyone:
> + /* Check which mask flags the ACE allows or denies. */
> + if (richace_is_deny(ace))
> + denied |= ace_mask & mask;
> + mask &= ~ace_mask;
> +
> + /*
> +  * Keep going until we know which file class
> +  * the process is in.
> +  */
> + if (!mask && in_owner_or_group_class)
> + break;
> + }
> + denied |= mask;
> +
> + if (acl->a_flags & RICHACL_MASKED) {
> + /*
> +  * The file class a process is in determines which file mask
> +  * applies.  Check if that file mask also grants the requested
> +  * access.
> +  */
> + if (uid_eq(current_fsuid(), inode->i_uid))
> + denied |= requested & ~acl->a_owner_mask;
> + else if (in_owner_or_group_class)
> + denied |= requested & ~acl->a_group_mask;
> + else {
> + if (acl->a_flags & RICHACL_WRITE_THROUGH)
> + denied = requested & ~acl->a_other_mask;
> + else
> + denied |= requested & ~acl->a_other_mask;
> + }
> + }
> +
> +out:
> + return denied ? -EACCES : 0;
> +}
> +EXPORT_SYMBOL_GPL(richacl_permission);
> diff --git a/include/linux/richacl.h b/include/linux/richacl.h
> index 3559b2c..be9fb65 100644
> --- a/include/linux/richacl.h
> +++ b/include/linux/richacl.h
> @@ -179,5 +179,6 @@ extern int richacl_masks_to_mode(const struct richacl *);
>  extern unsigned int richacl_mode_to_mask(umode_t);
>  extern unsigned int richacl_want_to_mask(unsigned int);
>  extern void richacl_compute_max_masks(struct richacl *);
> +extern int richacl_permission(struct inode *, const struct richacl *, int);
>
>  #endif /* __RICHACL_H */

Reviewed-by: Jeff Layton <jlayton@redhat.com>