ping
FWIW, this problem actually came up with an archive containing a fsroot
including a busybox installation again, but this time, the archive was
created after a deduplication step had hardlinked identical files and
symlinks.
On 4/1/18 1:37 PM, Harald van Dijk wrote:
When the creation of symlinks got delayed until after all other files
had been extracted, that didn't take into account that the archive may
contain hardlinks to those symlinks. The extraction of those hardlinks
did not get delayed so would fail.
This patch generalises the symlink_placeholders approach to a
link_placeholders which allows delaying the extraction of hardlinks too.
It changes the order in which delayed links are added to ensure that a
hardlink to an earlier symlink will create the symlink first.
It delays all hardlinks without regards to the target. It may be
desirable to instead tweak it to determine whether the link target is a
delayed symlink, but that is a cost/benefits tradeoff. As hardlinks are
relatively rare, I guess the benefit of such an optimisation would be
small, but I am not really qualified to make that determination.
Test case:
mkdir dir
>dir/a
ln -s ../dir/a dir/b
ln dir/b dir/c
mkdir new
tar cf - dir/* | tar -C new -xf -
busybox ad4e9613:
tar: can't create hardlink 'dir/c' to 'dir/b': No such file or directory
busybox ad4e9613 + patch:
No error output. The archive is successfully extracted.
The security hole that the delayed extraction of symlinks was meant to
prevent should not be re-introduced by the delayed creation of
hardlinks: the parent components of archive entries still get created
first, so if an archive contains a file "exploit", a symlink "parent ->
..", and a hardlink "parent/exploit -> exploit", the presence of that
hardlink causes "parent" to be immediately created as a regular
directory. The symlink creation "parent -> .." will therefore fail. This
could use careful review though.
Cheers,
Harald van Dijk
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