From: "J. Bruce Fields" Subject: Re: [PATCH v8 09/41] richacl: Update the file masks in chmod() Date: Mon, 28 Sep 2015 11:28:06 -0400 Message-ID: <20150928152806.GC1358@fieldses.org> References: <1443391772-10171-1-git-send-email-agruenba@redhat.com> <1443391772-10171-10-git-send-email-agruenba@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Alexander Viro , Theodore Ts'o , Andreas Dilger , Jeff Layton , Trond Myklebust , Anna Schumaker , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-api@vger.kernel.org To: Andreas Gruenbacher Return-path: Content-Disposition: inline In-Reply-To: <1443391772-10171-10-git-send-email-agruenba@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Mon, Sep 28, 2015 at 12:09:00AM +0200, Andreas Gruenbacher wrote: > Doing a chmod() sets the file mode, which includes the file permission > bits. When a file has a richacl, the permissions that the richacl > grants need to be limited to what the new file permission bits allow. > > This is done by setting the file masks in the richacl to what the file > permission bits map to. The richacl access check algorithm takes the > file masks into account, which ensures that the richacl cannot grant too > many permissions. > > It is possible to explicitly add permissions to the file masks which go > beyond what the file permission bits can grant (like the > RICHACE_WRITE_ACL permission). The POSIX.1 standard calls this an > alternate file access control mechanism. A subsequent chmod() would > ensure that those permissions are disabled again. > > Signed-off-by: Andreas Gruenbacher > Reviewed-by: J. Bruce Fields > --- > fs/richacl_base.c | 40 ++++++++++++++++++++++++++++++++++++++++ > include/linux/richacl.h | 1 + > 2 files changed, 41 insertions(+) > > diff --git a/fs/richacl_base.c b/fs/richacl_base.c > index fc544f7..6c69234 100644 > --- a/fs/richacl_base.c > +++ b/fs/richacl_base.c > @@ -339,3 +339,43 @@ restart: > acl->a_flags &= ~(RICHACL_WRITE_THROUGH | RICHACL_MASKED); > } > EXPORT_SYMBOL_GPL(richacl_compute_max_masks); > + > +/** > + * richacl_chmod - update the file masks to reflect the new mode > + * @mode: new file permission bits including the file type > + * > + * Return a copy of @acl where the file masks have been replaced by the file > + * masks corresponding to the file permission bits in @mode, or returns @acl > + * itself if the file masks are already up to date. Takes over a reference > + * to @acl. > + */ > +struct richacl * > +richacl_chmod(struct richacl *acl, mode_t mode) > +{ > + unsigned int x = S_ISDIR(mode) ? 0 : RICHACE_DELETE_CHILD; > + unsigned int owner_mask, group_mask, other_mask; > + struct richacl *clone; > + > + owner_mask = richacl_mode_to_mask(mode >> 6) & ~x; > + group_mask = richacl_mode_to_mask(mode >> 3) & ~x; > + other_mask = richacl_mode_to_mask(mode) & ~x; > + > + if (acl->a_owner_mask == owner_mask && > + acl->a_group_mask == group_mask && > + acl->a_other_mask == other_mask && > + (acl->a_flags & (RICHACL_WRITE_THROUGH | RICHACL_MASKED))) I think you meant to require both of those bits to be set. --b. > + return acl; > + > + clone = richacl_clone(acl, GFP_KERNEL); > + richacl_put(acl); > + if (!clone) > + return ERR_PTR(-ENOMEM); > + > + clone->a_flags |= (RICHACL_WRITE_THROUGH | RICHACL_MASKED); > + clone->a_owner_mask = owner_mask; > + clone->a_group_mask = group_mask; > + clone->a_other_mask = other_mask; > + > + return clone; > +} > +EXPORT_SYMBOL_GPL(richacl_chmod); > diff --git a/include/linux/richacl.h b/include/linux/richacl.h > index e81144a..e00f313 100644 > --- a/include/linux/richacl.h > +++ b/include/linux/richacl.h > @@ -298,5 +298,6 @@ extern int richacl_masks_to_mode(const struct richacl *); > extern unsigned int richacl_mode_to_mask(mode_t); > extern unsigned int richacl_want_to_mask(unsigned int); > extern void richacl_compute_max_masks(struct richacl *); > +extern struct richacl *richacl_chmod(struct richacl *, mode_t); > > #endif /* __RICHACL_H */ > -- > 2.4.3