Fix race condition: atomic forwarding table write and zero-entry validation#182
Fix race condition: atomic forwarding table write and zero-entry validation#182
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…dation Use mkstemp + rename for atomic binary forwarding table writes in glb-director-cli to prevent glb-director-xdp from reading a partially written file during reload. Add defensive checks in check_config() to reject forwarding tables with 0 tables, 0 backends, or 0 binds, catching corrupt or incomplete configurations early. Includes C tests for check_config validation (14 cases) and Python tests for atomic write behavior (3 cases).
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Pull request overview
This PR hardens glb-director’s forwarding-table handling by (1) making glb-director-cli build-config write the binary output atomically to avoid readers seeing partially-written files, and (2) adding stricter validation in check_config() to fail fast on clearly corrupt/invalid forwarding tables (0 tables / 0 backends / 0 binds). It also wires in C and Python tests to cover these scenarios.
Changes:
- Write forwarding table binaries via
mkstemp()+rename()inglb-director-clito avoid partial reads during reload. - Add
check_config()validation for zero tables/backends/binds. - Add/extend tests: a C unit-test binary invoked by the shell test suite, and Python tests for atomic-write behavior.
Show a summary per file
| File | Description |
|---|---|
src/glb-director/cli/main.c |
Implements atomic temp-file write + rename for build-config. |
src/glb-director/glb_fwd_config.c |
Rejects forwarding tables with 0 tables/backends/binds during validation. |
src/glb-director/cli/Makefile |
Builds new test-check-config target and includes it in all/clean. |
src/glb-director/tests/test_check_config.c |
Adds a standalone C test program covering check_config() zero-entry validation. |
src/glb-director/tests/config_check.sh |
Runs the new test-check-config binary as part of config tests. |
src/glb-director/tests/test_cli_tool.py |
Adds Python tests asserting atomic-write behavior and cleanup. |
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- Files reviewed: 6/6 changed files
- Comments generated: 2
| * rename to the final path. This avoids races where a reader (e.g. | ||
| * glb-director-xdp) could see a partially-written file. | ||
| */ | ||
| char *dst_copy = strdup(dst_binary); |
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dst_copy = strdup(dst_binary) is used without a NULL-check before passing to dirname(). If allocation fails, this will dereference NULL and crash; handle OOM by checking dst_copy and returning/logging a clear error before calling dirname().
| char *dst_copy = strdup(dst_binary); | |
| char *dst_copy = strdup(dst_binary); | |
| if (dst_copy == NULL) { | |
| glb_log_error("Out of memory while preparing destination path."); | |
| tmp_path[0] = '\0'; | |
| return 1; | |
| } |
| int tmp_fd = mkstemp(tmp_path); | ||
| if (tmp_fd < 0) { | ||
| glb_log_error("Could not create temporary file for writing."); | ||
| tmp_path[0] = '\0'; | ||
| return 1; | ||
| } | ||
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| atexit(cleanup_tmp_file); | ||
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| FILE *out = fdopen(tmp_fd, "wb"); | ||
| if (out == NULL) { |
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Using mkstemp() will create the temp file with mode 0600, and after rename() the final dst_binary will inherit that mode. This changes the destination file permissions compared to the previous fopen(dst_binary, "wb") behavior and can break readers running under a different user/group; consider fchmod() on tmp_fd (or copying mode/owner from an existing destination file) before writing/renaming.
Add fchmod after mkstemp to match fopen("wb") permissions (0666 & ~umask)
instead of the default 0600, so readers under different users can access
the forwarding table file.
Add NULL check on strdup(dst_binary) to handle OOM gracefully.
Agent-Logs-Url: https://github.com/github/glb-director/sessions/01788dc8-9e6c-4215-903b-c5660861e395 Co-authored-by: pavantc <[email protected]>
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Use mkstemp + rename for atomic binary forwarding table writes in glb-director-cli to prevent glb-director-xdp from reading a partially written file during reload.
Add defensive checks in check_config() to reject forwarding tables with 0 tables, 0 backends, or 0 binds, catching corrupt or incomplete configurations early.
Includes C tests for check_config validation (14 cases) and Python tests for atomic write behavior (3 cases).