TapTap
b216ed31fb
- H3: a daemon module without 'client owner = yes' now also has super-user device activity forced off (char/block mknod, --write-devices), so a root daemon can no longer be made to create/write raw devices under AUTO. The entries are skipped, preserving ordinary -a pushes. - H1/H2: propagate a failed required --copy-as chown from symlink metadata restore and implicitly-created parent directories, so the entry (and run) reports failure instead of a wrong-owner success. - Docs/help/headers updated for A2/A3 and the device clamp; startup warning spells out the client-owner risk. - Tests: daemon device clamp (skipped without opt-in, created with opt-in), updated --super/--fake-super expectations.
101 lines
4.9 KiB
C
101 lines
4.9 KiB
C
#ifndef XATTR_H
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#define XATTR_H
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#include <stdbool.h>
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#include <stddef.h>
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#include <stdint.h>
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/*
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* Portable extended-attribute (xattr) and POSIX-ACL preservation (Phase 4,
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* protocol 2.13.0). --xattrs/-X and --acls/-A are implemented on top of the
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* xattr machinery: the SENDER captures a bounded, namespace-whitelisted set of
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* `name = value` pairs per file, transmits them in a per-file wire block, and
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* the RECEIVER re-applies them fd-relative on the just-written file. Linux
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* xattr syscalls are used; libacl is NOT required (ACLs travel as the
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* system.posix_acl_access / system.posix_acl_default xattrs).
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*
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* Security model:
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* * A client can never force a `security.*` / privileged xattr onto the
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* destination: both capture (sender) and apply (receiver) are restricted to
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* the unprivileged `user.*` namespace and the two POSIX ACL xattrs. The
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* receiver independently re-validates every incoming name against this
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* whitelist, so a malicious sender's `security.capability` payload is
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* rejected, not applied.
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* * Payloads are bounded (per-name length, per-value length, per-file count
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* and total bytes) on BOTH ends to prevent OOM/memory abuse; an oversized
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* or malformed frame is a clean protocol rejection, never an allocation
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* blowup.
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* * Application is confined to the exact destination file descriptor
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* (fsetxattr on the just-written fd), never a caller-controlled path.
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*/
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/* Reserved key used by --fake-super to park the source's privileged ownership
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* / mode / mtime on the destination file as an unprivileged user.* xattr, so a
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* later privileged restore could re-apply them. Exact documented format:
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* uid:gid:mode:mtime_sec:mtime_nsec (decimal, decimal, octal, dec, dec)
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* e.g. "1000:1000:644:1765238400:0". */
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#define FAKESUPER_XATTR "user.fastsync.stat"
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/* --- bounds --- */
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#define XATTR_NAME_MAX 255 /* xattr names are limited to 255 bytes */
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#define XATTR_VALUE_MAX (1024 * 1024) /* per-value cap (1 MiB) */
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#define XATTR_TOTAL_MAX (4 * 1024 * 1024) /* per-file total name+value bytes */
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#define XATTR_MAX_COUNT 256
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typedef struct {
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char* name; /* owned, NUL-terminated */
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unsigned char* value; /* owned, may hold embedded NULs */
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size_t value_len;
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} FileXattr;
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typedef struct {
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FileXattr* items;
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int count;
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} FileXattrList;
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FileXattrList* xattr_list_new(void);
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void xattr_list_free(FileXattrList* list);
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/* Append one entry (deep copy). Returns false on allocation failure. */
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bool xattr_list_append(FileXattrList* list, const char* name, const void* value, size_t value_len);
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/* True when `name` is a well-formed xattr name AND belongs to a namespace this
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* build is authorized to apply (user.* or the two POSIX ACL xattrs). Used for
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* both capture and receiver-side validation. */
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bool xattr_name_appliable(const char* name);
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/* Sender: read the whitelisted xattrs of `path` into a new list. Returns NULL
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* when the path has no appliable xattrs (or the filesystem has no xattr
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* support); an empty-but-valid list is never returned distinct from NULL. */
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FileXattrList* xattr_capture_path(const char* path);
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/* Wire: bounded serialization. xattr_send returns false on write failure; an
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* empty/NULL list transmits a zero-count block. xattr_receive returns NULL and
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* sets *ok = 0 on any malformed / oversized / non-whitelisted entry. */
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bool xattr_send(int fd, const FileXattrList* list);
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FileXattrList* xattr_receive(int fd, int* ok);
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/* Receiver: apply every entry fd-relative (fsetxattr) to the just-written file
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* descriptor. A per-attribute failure (e.g. ACL set refused for non-root on a
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* file the process does not own) is logged and skipped, never fatal. Returns
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* true when apply was attempted (allowing callers to treat it as best-effort). */
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bool xattr_apply_fd(int fd, const FileXattrList* list);
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/* --fake-super: write the source uid/gid/mode/mtime record into the reserved
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* FAKESUPER_XATTR on `fd`. Best-effort (logged, never fatal). Only meaningful
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* when metadata was transmitted so the values exist. */
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void fake_super_store_fd(int fd, uint32_t uid, uint32_t gid, uint32_t mode, int64_t mtime_sec,
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int64_t mtime_nsec);
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/* --fake-super replay: parse the FAKESUPER_XATTR record previously written on
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* `fd` by fake_super_store_fd and re-apply uid/gid/mode/mtime fd-relative.
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* Best-effort: absence of the xattr or a malformed record is a silent no-op
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* that never fails the transfer. The OWNER leg is applied only when an explicit
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* ownership identity policy is active (numeric-ids/chown/usermap/groupmap/
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* copy-as), when super-user activities are permitted, and when --copy-as is not
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* authoritative; a non-root EPERM/EACCES is skipped silently, matching
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* FastSync's identity philosophy. The mode is sanitized exactly like the normal
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* metadata path (group/other write bits never granted). Returns true when the
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* xattr was present and parsed. */
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bool fake_super_restore_fd(int fd);
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#endif |