Don't Forget the ZFS "aclinherit" Property

/dont-forget-the-zfs-aclinherit-property 2012-03-29T18:35:35+01:00

A colleague posed an interesting issue his customer was having. They were finding their ACLs were not being passed onto the files created within the directory they'd applied the ACLs to, even through they had set the inheritance ACLs as desired.

This is what they were doing and seeing.

First they were creating a directory and setting the ACLs on that directory:

# mkdir /export/testdir
# chmod A+user:bob:rwx:fd:allow /export/testdir
# chmod A+user:dave:rwx:fd:allow /export/testdir
# ls -dV /export/testdir
drwxr-xr-x+  2 root     root           2 Mar 27 09:10 /export/testdir
              user:dave:rwx-----------:fd-----:allow
               user:bob:rwx-----------:fd-----:allow
                 owner@:rwxp-DaARWcCos:-------:allow
                 group@:r-x---a-R-c--s:-------:allow
              everyone@:r-x---a-R-c--s:-------:allow
#

Note, the fd part is the inheritance flags. From the chmod(1) man page:

     The optional inheritance flags can be specified in the three
     formats. The first format uses words to indicate the various
     inheritance flags separated with a forward slash (/) charac-
     ter.

     file_inherit (f)    Inherit to all newly created files.

     dir_inherit (d)     Inherit  to  all  newly  created  direc-
                         tories.

This all looks good, until the user bob or dave create a file in /export/testdir and the other user tries to update it...

# su - bob -c "echo bob > /export/testdir/file"
Oracle Corporation	SunOS 5.11	11.0	January 2012
# su - dave -c "echo dave >> /export/testdir/file"
Oracle Corporation	SunOS 5.11	11.0	January 2012
-bash: /export/testdir/file: Permission denied
#

The permission denied error was certainly not expected. Closer examination of the ACL of this new file shows...

# ls -V /export/testdir/file
-rw-r--r--+  1 bob      staff          4 Mar 27 09:14 /export/testdir/file
              user:dave:r-------------:------I:allow
               user:bob:rw------------:------I:allow
                 owner@:rw-p--aARWcCos:-------:allow
                 group@:r-----a-R-c--s:-------:allow
              everyone@:r-----a-R-c--s:-------:allow
#

Looks like the ACL created on the directory hasn't been inherited by the file. Now this is the part he and his customer couldn't understand.

I had a quick look at this and I realised the problem was with inheritance. One thing many people forget when using ACL inheritance is ZFS be default restricts inheritance and in fact strips out the write_owner and write_acl permissions when an ACL entry is inherited. This is exactly what has happened above.

Both my colleague and the customer forgot one important thing: the aclinherit property of the ZFS filesystem in question. A quick look at this revealed it was indeed restricted:

# zfs get aclinherit rpool/export
NAME          PROPERTY    VALUE          SOURCE
rpool/export  aclinherit  restricted     default
#

Changing this to passthrough...

# zfs set aclinherit=passthrough rpool/export
# zfs get aclinherit rpool/export
NAME          PROPERTY    VALUE          SOURCE
rpool/export  aclinherit  passthrough    local
#

... and performing the above again...

# rm /export/testdir/file
# su - bob -c "echo bob > /export/testdir/file"
Oracle Corporation	SunOS 5.11	11.0	January 2012
# su - dave -c "echo dave >> /export/testdir/file"
Oracle Corporation	SunOS 5.11	11.0	January 2012
# cat /export/testdir/file
bob
dave
# ls -V /export/testdir/file
-rwxr--r--+  1 bob      staff          9 Mar 27 09:21 /export/testdir/file
              user:dave:rwx-----------:------I:allow
               user:bob:rwx-----------:------I:allow
                 owner@:rw-p--aARWcCos:-------:allow
                 group@:r-----a-R-c--s:-------:allow
              everyone@:r-----a-R-c--s:-------:allow
#

... has the desired effect. It has worked without error and the new file has the desired ACL.

So in summary, when using ACLs on ZFS filesystems with inheritance, don't forget to set the aclinherit property appropriately. More details on the aclinherit property can be found in the ZFS Admin Guide.

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