diff mbox

[v11,16/48] richacl: Automatic Inheritance

Message ID 1445008706-15115-17-git-send-email-agruenba@redhat.com
State New, archived
Headers show

Commit Message

Andreas Gruenbacher Oct. 16, 2015, 3:17 p.m. UTC
Automatic Inheritance (AI) allows changes to the acl of a directory to
propagate down to children.

This is mostly implemented in user space: when a process changes the
permissions of a directory and Automatic Inheritance is enabled for that
directory, the process must propagate those changes to all children,
recursively.

The kernel enables this by keeping track of which permissions have been
inherited at create time.  In addition, it makes sure that permission
propagation is turned off when the permissions are set explicitly (for
example, upon create or chmod).

Automatic Inheritance works as follows:

 - When the RICHACL_AUTO_INHERIT flag in the acl of a file or directory
   is not set, the file or directory is not affected by AI.

 - When the RICHACL_AUTO_INHERIT flag in the acl of a directory is set
   and a file or subdirectory is created in that directory, the
   inherited acl will have the RICHACL_AUTO_INHERIT flag set, and all
   inherited aces will have the RICHACE_INHERITED_ACE flag set.  This
   allows user space to distinguish between aces which have been
   inherited and aces which have been explicitly added.

 - When the RICHACL_PROTECTED acl flag in the acl of a file or directory
   is set, AI will not modify the acl.  This does not affect propagation
   of permissions from the file to its children (if the file is a
   directory).

Linux does not have a way of creating files or directories without setting the
file permission bits, so all files created inside a directory with
RICHACL_AUTO_INHERIT set will have the RICHACL_PROTECTED flag set.  This
effectively disables Automatic Inheritance.

Protocols which support creating files without specifying permissions can
explicitly clear the RICHACL_PROTECTED flag after creating a file and reset the
file masks to "undo" applying the create mode; see richacl_compute_max_masks().
They should set the RICHACL_DEFAULTED flag.  (A mechanism that would allow to
indicate to the kernel to ignore the create mode in the first place when there
are inherited permissions would be nice to have.)

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/richacl_base.c       | 10 +++++++++-
 fs/richacl_inode.c      |  7 +++++++
 include/linux/richacl.h | 19 ++++++++++++++++++-
 3 files changed, 34 insertions(+), 2 deletions(-)

Comments

Andy Lutomirski Oct. 16, 2015, 4 p.m. UTC | #1
On Fri, Oct 16, 2015 at 8:17 AM, Andreas Gruenbacher
<agruenba@redhat.com> wrote:
> Automatic Inheritance (AI) allows changes to the acl of a directory to
> propagate down to children.
>
> This is mostly implemented in user space: when a process changes the
> permissions of a directory and Automatic Inheritance is enabled for that
> directory, the process must propagate those changes to all children,
> recursively.
>
> The kernel enables this by keeping track of which permissions have been
> inherited at create time.  In addition, it makes sure that permission
> propagation is turned off when the permissions are set explicitly (for
> example, upon create or chmod).
>
> Automatic Inheritance works as follows:
>
>  - When the RICHACL_AUTO_INHERIT flag in the acl of a file or directory
>    is not set, the file or directory is not affected by AI.
>
>  - When the RICHACL_AUTO_INHERIT flag in the acl of a directory is set
>    and a file or subdirectory is created in that directory, the
>    inherited acl will have the RICHACL_AUTO_INHERIT flag set, and all
>    inherited aces will have the RICHACE_INHERITED_ACE flag set.  This
>    allows user space to distinguish between aces which have been
>    inherited and aces which have been explicitly added.

What if the file or subdirectory that's created in that directory is a
hard link?

--Andy
--
To unsubscribe from this list: send the line "unsubscribe linux-cifs" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Andreas Gruenbacher Oct. 16, 2015, 4:13 p.m. UTC | #2
On Fri, Oct 16, 2015 at 6:00 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Fri, Oct 16, 2015 at 8:17 AM, Andreas Gruenbacher
> <agruenba@redhat.com> wrote:
>> Automatic Inheritance works as follows:
>>
>>  - When the RICHACL_AUTO_INHERIT flag in the acl of a file or directory
>>    is not set, the file or directory is not affected by AI.
>>
>>  - When the RICHACL_AUTO_INHERIT flag in the acl of a directory is set
>>    and a file or subdirectory is created in that directory, the
>>    inherited acl will have the RICHACL_AUTO_INHERIT flag set, and all
>>    inherited aces will have the RICHACE_INHERITED_ACE flag set.  This
>>    allows user space to distinguish between aces which have been
>>    inherited and aces which have been explicitly added.
>
> What if the file or subdirectory that's created in that directory is a
> hard link?

Directories cannot have hard links.

When a file is hard linked into multiple directories with different
inheritable permissions, the permissions set last will "win". This
isn't particularly pretty, but it's the way this has worked on that
other operating system with significant marked share for the last
fifteen years.

Thanks,
Andreas
--
To unsubscribe from this list: send the line "unsubscribe linux-cifs" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
diff mbox

Patch

diff --git a/fs/richacl_base.c b/fs/richacl_base.c
index cb5081e..3a97a82 100644
--- a/fs/richacl_base.c
+++ b/fs/richacl_base.c
@@ -366,7 +366,8 @@  __richacl_chmod(struct richacl *acl, umode_t mode)
 	    acl->a_group_mask == group_mask &&
 	    acl->a_other_mask == other_mask &&
 	    (acl->a_flags & RICHACL_MASKED) &&
-	    (acl->a_flags & RICHACL_WRITE_THROUGH))
+	    (acl->a_flags & RICHACL_WRITE_THROUGH) &&
+	    (!richacl_is_auto_inherit(acl) || richacl_is_protected(acl)))
 		return acl;
 
 	clone = richacl_clone(acl, GFP_KERNEL);
@@ -378,6 +379,8 @@  __richacl_chmod(struct richacl *acl, umode_t mode)
 	clone->a_owner_mask = owner_mask;
 	clone->a_group_mask = group_mask;
 	clone->a_other_mask = other_mask;
+	if (richacl_is_auto_inherit(clone))
+		clone->a_flags |= RICHACL_PROTECTED;
 
 	return clone;
 }
@@ -551,6 +554,11 @@  richacl_inherit(const struct richacl *dir_acl, int isdir)
 			ace++;
 		}
 	}
+	if (richacl_is_auto_inherit(dir_acl)) {
+		acl->a_flags = RICHACL_AUTO_INHERIT;
+		richacl_for_each_entry(ace, acl)
+			ace->e_flags |= RICHACE_INHERITED_ACE;
+	}
 
 	return acl;
 }
diff --git a/fs/richacl_inode.c b/fs/richacl_inode.c
index 4f3a1b7..b88a2f1 100644
--- a/fs/richacl_inode.c
+++ b/fs/richacl_inode.c
@@ -277,6 +277,13 @@  richacl_inherit_inode(const struct richacl *dir_acl, umode_t *mode_p)
 			richacl_put(acl);
 			acl = NULL;
 		} else {
+			/*
+			 * We need to set RICHACL_PROTECTED because we are
+			 * doing an implicit chmod
+			 */
+			if (richacl_is_auto_inherit(acl))
+				acl->a_flags |= RICHACL_PROTECTED;
+
 			richacl_compute_max_masks(acl);
 			/*
 			 * Ensure that the acl will not grant any permissions
diff --git a/include/linux/richacl.h b/include/linux/richacl.h
index d7e10aa..67843a6 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -41,6 +41,9 @@  struct richacl {
 };
 
 #define RICHACL_VALID_FLAGS (					\
+	RICHACL_AUTO_INHERIT |					\
+	RICHACL_PROTECTED |					\
+	RICHACL_DEFAULTED |					\
 	RICHACL_WRITE_THROUGH |					\
 	RICHACL_MASKED)
 
@@ -50,13 +53,15 @@  struct richacl {
 	RICHACE_NO_PROPAGATE_INHERIT_ACE |			\
 	RICHACE_INHERIT_ONLY_ACE |				\
 	RICHACE_IDENTIFIER_GROUP |				\
+	RICHACE_INHERITED_ACE |					\
 	RICHACE_SPECIAL_WHO)
 
 #define RICHACE_INHERITANCE_FLAGS (				\
 	RICHACE_FILE_INHERIT_ACE |				\
 	RICHACE_DIRECTORY_INHERIT_ACE |				\
 	RICHACE_NO_PROPAGATE_INHERIT_ACE |			\
-	RICHACE_INHERIT_ONLY_ACE )
+	RICHACE_INHERIT_ONLY_ACE |				\
+	RICHACE_INHERITED_ACE)
 
 /* Valid RICHACE_* flags for directories and non-directories */
 #define RICHACE_VALID_MASK (					\
@@ -113,6 +118,18 @@  extern void set_cached_richacl(struct inode *, struct richacl *);
 extern void forget_cached_richacl(struct inode *);
 extern struct richacl *get_richacl(struct inode *);
 
+static inline int
+richacl_is_auto_inherit(const struct richacl *acl)
+{
+	return acl->a_flags & RICHACL_AUTO_INHERIT;
+}
+
+static inline int
+richacl_is_protected(const struct richacl *acl)
+{
+	return acl->a_flags & RICHACL_PROTECTED;
+}
+
 /**
  * richace_is_owner  -  check if @ace is an OWNER@ entry
  */