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Zhengchao An
c1b8136f9a
The Local backend's durability argument rests on properties of the filesystem it runs on, and those properties were assumptions: the crate had no test touching symlinks, none asserting a published file's mode, and none on directory replacement or cross-device behavior. Writing that verification surfaced three gaps. The key directory's own permissions were never set and never read. create_dir_all applies the process umask, which is 0 in a good many container images, and the platform picks the mode far more often than an operator does: kubelet creates an emptyDir 0777, several PVC provisioners mkdir -m 0777, a --tmpfs mount lands at 1777. Write access there is the power to delete a key, destroying every object it protects, or to plant a record for a key id that does not exist yet. The directory is now created 0700 through DirBuilder::mode, so intermediate components are covered and no create-then-chmod window exists, and anything wider is narrowed on every start and re-read to confirm it took. Narrowing rather than refusing matches what the observability stack already does with its own directory; refusing would turn each of those platform defaults into a server that will not start while leaving the exposure on disk. Only a directory this process cannot secure is fatal. An unspecified file_permissions meant whatever the umask said. The field is optional in the persisted configuration and stays optional, but with it absent the entire mode-application block was skipped, so under a 0 umask master key records were published world-readable. Absent now resolves to owner-only inside the commit protocol rather than at each call site, so the backup restore path — which passed the unset value straight through and published a legacy cluster's restored records at 0644 — is covered by construction. Startup left symlinked commit temps behind forever, because the orphan sweep required a regular file. The protocol only ever creates temps with create_new, so an entry wearing a temp name and any other file type is either its own leftover or something planted. Eight tests pin the boundaries: that a requested mode survives the umask, that an absent one still resolves owner-only, that a directory at each mode a real platform produces is narrowed, that publishing replaces a symlink instead of writing through it on both the hard_link and rename paths, that a planted hard link cannot be adopted as a key record, that a symlinked commit temp is removed without harming the key it pointed at, and that commit temps never leave the destination's directory. A real cross-device operation and a directory swapped between rename and fsync cannot be verified without a second filesystem and directory file descriptors respectively; both are recorded in the operations documentation rather than left looking covered.