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[Bug-tar] ACL support, extract and default ACLs

From: Markus Steinborn
Subject: [Bug-tar] ACL support, extract and default ACLs
Date: Sun, 05 Jun 2016 21:26:14 +0200
User-agent: Mozilla/5.0 (X11; Linux i686; rv:28.0) Gecko/20100101 Firefox/28.0 SeaMonkey/2.25


I'd like to remember the following bug report. I've ported the patches for it to GNU tar 1.29.

Also see https://bugzilla.redhat.com/show_bug.cgi?id=1052876

Storing and restoring ACLs in tar archives should be improved:

(1) tar archive creation with "--numeric-owner" option:

In this case, users are expectiing that the archive does not contain any symbolic owner name, so it can be extracted to an emoty hard disc on a system bootet e. g. by a rescue cd from Redhat. Current sitation is that ACLs still include the symbolic owner and not the numeric owner.

This is quite trivial to fix (not completely contained in the attached patches):

Replace all ocurences of "val = acl_to_text(acl, &len);" by "val = acl_to_any_text(acl, 0, ',', ( numeric_owner_option?TEXT_NUMERIC_IDS:0));" and followed by "len=strlen(val);" after the "if (!val)" error-handling.

Effect: Numeric owner is stored.

I'd like to note that this improvement is essential to me.

(2a) tar archive creation without "--numeric-owner" option:

In GNU tar 1.26, for every file the owner is stored both, symbolic and numeric. I would expect that ACLs are stored in both ways, too. star shows us how to do that:

star stores the numeric owner in a forth field of an acl: (e.g. "u:msteinbo:rwx:500").

(2b) tar extract should use the 4th field (discussed in point 2) in presence of "-numeric-owner".

This together with point (2) enabled users to restore an backup created without numeric owner option on a clean hard disc without passwd entries for the users (let's assume that /etc/passwd is contained in the archive so the operation makes sense).

I'd like to mention that this point would increase star compatibility a lot.

(see also http://lists.gnu.org/archive/html/bug-tar/2013-03/msg00021.html
upstream maintainer "Paul Eggert" says in
"That sort of thing all sounds reasonable, I guess. I'd like Sergey's opinion though.".

Greetings from Germany

Markus Steinborn
GNU gv maintainer

Attachment: 0001-tar-extract-should-use-the-4th-field-discussed-in-po.patch
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Attachment: 0002-tar-archive-creation-without-numeric-owner-option.patch
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Attachment: 0003-Do-not-store-filesystem-dependent-xattrs-i.e.-ACLs-e.patch
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