fix: additional checks for tmp fallback file in shmem - #2458
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| fn fallback_path<P: ?Sized + NixPath>(name: &P) -> nix::Result<CString> { | ||
| name.with_nix_path(|cstr| { | ||
| let mut path = "/tmp/libdatadog".to_string().into_bytes(); | ||
| let mut path = format!("/tmp/libdatadog-{}", getuid().as_raw()).into_bytes(); |
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When the sidecar master runs as root and workers run under another UID, the initialization in datadog-sidecar/src/setup/thread_listener.rs calls set_shm_owner_uid(cred.uid) specifically to make the shared-memory file accessible across users. In a fallback environment such as AWS Lambda, however, the master now creates the file under /tmp/libdatadog-0, while the worker's NamedShmHandle::open computes /tmp/libdatadog-<worker uid> and therefore cannot find it; the directory's 0700 mode would also prevent traversal even if both used the master's path. This breaks all named cross-user IPC whenever POSIX shm_open is unavailable, so creation should select a namespace that the intended owner will also use and can traverse.
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Hmm, indeed, if the sidecar and the worker can be run under different users, this makes things harder than I thought. Wdyt @bwoebi ? Do workers and the sidecar always run under the same user?
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🔒 Cargo Deny Results📦
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BenchmarksComparisonBenchmark execution time: 2026-09-03 12:33:33 Comparing candidate commit ea4400a in PR branch Found 0 performance improvements and 0 performance regressions! Performance is the same for 2 metrics, 0 unstable metrics.
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| cpu_model | git_commit_sha | git_commit_date | git_branch |
|---|---|---|---|
| Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz | ea4400a | 1788436400 | yannham/APMSP-3157 |
| scenario | metric | min | mean ± sd | median ± mad | p75 | p95 | p99 | max | peak_to_median_ratio | skewness | kurtosis | cv | sem | runs | sample_size |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| write only interface | execution_time | 2.038µs | 2.060µs ± 0.005µs | 2.060µs ± 0.003µs | 2.063µs | 2.068µs | 2.071µs | 2.080µs | 1.00% | -0.316 | 2.777 | 0.26% | 0.000µs | 1 | 200 |
| scenario | metric | 95% CI mean | Shapiro-Wilk pvalue | Ljung-Box pvalue (lag=1) | Dip test pvalue |
|---|---|---|---|---|---|
| write only interface | execution_time | [2.059µs; 2.061µs] or [-0.037%; +0.037%] | None | None | None |
Group 2
| cpu_model | git_commit_sha | git_commit_date | git_branch |
|---|---|---|---|
| Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz | ea4400a | 1788436400 | yannham/APMSP-3157 |
| scenario | metric | min | mean ± sd | median ± mad | p75 | p95 | p99 | max | peak_to_median_ratio | skewness | kurtosis | cv | sem | runs | sample_size |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| two way interface | execution_time | 20.980µs | 21.675µs ± 0.252µs | 21.626µs ± 0.144µs | 21.810µs | 22.129µs | 22.464µs | 22.561µs | 4.32% | 0.897 | 1.288 | 1.16% | 0.018µs | 1 | 200 |
| scenario | metric | 95% CI mean | Shapiro-Wilk pvalue | Ljung-Box pvalue (lag=1) | Dip test pvalue |
|---|---|---|---|---|---|
| two way interface | execution_time | [21.640µs; 21.710µs] or [-0.161%; +0.161%] | None | None | None |
Baseline
Baseline benchmark details
Group 1
| cpu_model | git_commit_sha | git_commit_date | git_branch |
|---|---|---|---|
| Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz | efbbf4c | 1788373668 | main |
| scenario | metric | min | mean ± sd | median ± mad | p75 | p95 | p99 | max | peak_to_median_ratio | skewness | kurtosis | cv | sem | runs | sample_size |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| write only interface | execution_time | 2.037µs | 2.056µs ± 0.006µs | 2.056µs ± 0.003µs | 2.059µs | 2.064µs | 2.069µs | 2.097µs | 1.96% | 1.090 | 9.370 | 0.30% | 0.000µs | 1 | 200 |
| scenario | metric | 95% CI mean | Shapiro-Wilk pvalue | Ljung-Box pvalue (lag=1) | Dip test pvalue |
|---|---|---|---|---|---|
| write only interface | execution_time | [2.055µs; 2.057µs] or [-0.041%; +0.041%] | None | None | None |
Group 2
| cpu_model | git_commit_sha | git_commit_date | git_branch |
|---|---|---|---|
| Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz | efbbf4c | 1788373668 | main |
| scenario | metric | min | mean ± sd | median ± mad | p75 | p95 | p99 | max | peak_to_median_ratio | skewness | kurtosis | cv | sem | runs | sample_size |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| two way interface | execution_time | 20.665µs | 21.589µs ± 0.315µs | 21.525µs ± 0.143µs | 21.707µs | 22.152µs | 22.652µs | 23.566µs | 9.49% | 1.870 | 8.071 | 1.46% | 0.022µs | 1 | 200 |
| scenario | metric | 95% CI mean | Shapiro-Wilk pvalue | Ljung-Box pvalue (lag=1) | Dip test pvalue |
|---|---|---|---|---|---|
| two way interface | execution_time | [21.545µs; 21.633µs] or [-0.202%; +0.202%] | None | None | None |
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Artifact Size Benchmark Reportaarch64-alpine-linux-musl
aarch64-unknown-linux-gnu
libdatadog-x64-windows
libdatadog-x86-windows
x86_64-alpine-linux-musl
x86_64-unknown-linux-gnu
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What does this PR do?
This PR hardens the permissions set on the tmp fallback file created by the sidecar for IPC.
Motivation
See https://datadoghq.atlassian.net/browse/APMSP-3157.