Chmod preserve root - #10033
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sylvestre
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Jul 31, 2026
--preserve-root was only enforced for the paths named on the command line (the operand loop in Chmoder::chmod). With -R -L, a symlink encountered *inside* the tree that resolves to / was followed, and the recursion walked into the real root, defeating the failsafe. Reproduced in a sandboxed root: a tree containing `link -> /` with `chmod -R -L --preserve-root 777 tree` took an unrelated 0700 directory to 0777. GNU coreutils 9.10 refuses the same case. Re-check the guard at every descent, in both walk_dir_with_context variants so unix, non-unix and redox are all covered. Only symlinks are canonicalized, so ordinary recursive trees are unaffected. Behaviour now matches GNU: diagnose with the "(same as '/')" wording, skip the subtree, continue, and exit 1 -- rather than aborting the whole run. chown/chgrp already did this in 5c2c38c; chmod was the outlier. PR #10033 fixed only the operand-level "resolves to /" case.
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Previously the --preserve-root flag could be bypassed because it was only compared to "/" so anyhting that resolved to root but wasn't literally "/" would not be caught.
Also added regression test.
Fixes: #10018