Fix nmtree crashing with duplicate items

[renato.riolino_eldorado.org.br]

Summary

Bug: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=192839

If the addchild() function finds that the current item is already in the linked list, it overrides the duplicated item with the new one and then free() the new one, but the calling function would still reference the new item that was freed.

Test Plan

nmtree -dEU <<EOF

.
item
item
..
EOF

[brooks]

This should be submitted to NetBSD so we don't have to maintain a local diff.

contrib/mtree/spec.c

720

To reduce the churn of this patch, I'm tempted to suggest this should be centryp and there should be a NODE *centry that is initialized to *centry.

[renato.riolino_eldorado.org.br]

Fix for #192839 - Duplicate entries in an mtree file cause nmtree to coredump

[brooks]

You seem to be manually uploading diffs rather than using arcanist and the diff is now against your previous version not against the freebsd tree...

[renato.riolino_eldorado.org.br]

Diff now is against freebsd tree