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

[Andreas Gruenbacher]

On Tue, Jul 5, 2016 at 4:59 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
>> Reviewed-by: J. Bruce Fields <bfields@xxxxxxxxxxxx>
>> ---
>>  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 ?

Yes, thanks.

>> +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@xxxxxxxxxx>

Thanks,
Andreas