fix(fs): handle symlinks in overlay rename and copy#1014
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OverlayFs::rename and copy used read_file which intentionally doesn't follow symlinks (TM-ESC-002), causing silent failures when renaming or copying symlinks. Now detects symlinks via stat and preserves them as symlinks using read_link + symlink. Same fix applied to MountableFs cross-mount rename/copy.
Document the symlink rename/copy vulnerability in overlay and mountable filesystems. OverlayFs::rename used read_file which doesn't follow symlinks, silently failing. Now fixed and tracked as TM-ESC-016.
Cover MountableFs cross-mount paths for symlink rename and copy to ensure symlinks are preserved across filesystem boundaries.
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Summary
OverlayFs::renameandcopyusedread_file()which intentionally doesn't follow symlinks (TM-ESC-002), causing silent failures when operating on symlinks. Now detects symlinks viastat()and preserves them usingread_link()+symlink().MountableFscross-mount rename/copy paths.Test plan
overlay_rename_preserves_symlink— rename symlink in upper layeroverlay_rename_symlink_from_lower_layer— rename symlink from lower to upper (CoW)overlay_copy_preserves_symlink— copy preserves symlink typesymlink_rename_cannot_escape_mount_via_read— read_file on renamed symlink still blockedbash_mv_symlink_in_overlay— end-to-end mv + readlink in bash session