Check for SIG_IGN and SIG_DFL before calling previous signal handler by jtschuster · Pull Request #132900 · dotnet/runtime

jtschuster · 2026-08-28T18:00:35Z

macOS doesn't clear sa_flags when calling execve. When dotnet is started from a process that sets a signal handler, the handler is cleared, but not the sa_flags. When the runtime gets a signal from an external source, it sees a stale SA_SIGINGO and tries to call the previous signal handler, but the pointer is set to SIG_IGN or SIG_DFL, which causes a crash. This change checks for those values before calling the previous signal handler. Also adds a regression test for the issue.

Fixes #132581

macOS doesn't clear sa_flags when calling execve. When dotnet is started from a process that sets a signal handler, the handler is cleared, but not the sa_flags. When the runtime gets a signal from an external source, it sees a stale SA_SIGINGO and tries to call the previous signal handler, but the pointer is set to SIG_IGN or SIG_DFL, which causes a crash. This change checks for those values before calling the previous signal handler. Add a regression test for the issue.

azure-pipelines · 2026-08-28T18:01:23Z

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dotnet-policy-service · 2026-08-28T18:02:53Z

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Pull request overview

This PR hardens CoreCLR and NativeAOT activation-signal chaining by ensuring the runtime does not attempt to call a previous signal “handler” when the saved disposition is actually SIG_DFL or SIG_IGN, even if SA_SIGINFO is set (a state observed on macOS across execve). It also adds a macOS-only regression test that reproduces the inherited SA_SIGINFO + default/ignored disposition scenario and validates the runtime remains stable when an external SIGUSR1 arrives.

Changes:

CoreCLR: gate chaining to the saved activation signal disposition behind IsSigDfl/IsSigIgn checks before calling either sa_sigaction or sa_handler.
NativeAOT: apply the same SIG_DFL / SIG_IGN guard to activation handler chaining when SA_SIGINFO is set.
Tests: add a macOS-only regression test that installs an SA_SIGINFO handler, execvs into the .NET process, then triggers an external SIGUSR1 to exercise the chaining path.

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File	Description
src/coreclr/pal/src/exception/signal.cpp	Prevents calling the previous activation handler when it’s `SIG_DFL`/`SIG_IGN`, regardless of stale `SA_SIGINFO`.
src/coreclr/nativeaot/Runtime/unix/PalUnix.cpp	Mirrors the same `SIG_DFL`/`SIG_IGN` guard for NativeAOT’s activation handler chaining.
src/tests/Regressions/coreclr/GitHub_132581/test132581.csproj	Adds a macOS-only, process-isolated regression test project with a native CMake dependency.
src/tests/Regressions/coreclr/GitHub_132581/test132581.cs	Managed test that `execv`s after installing the signal handler and then triggers an external `SIGUSR1`.
src/tests/Regressions/coreclr/GitHub_132581/nativetest132581.cpp	Native helper to install the `SA_SIGINFO` handler + `execv`, and to send `SIGUSR1` from a forked child.
src/tests/Regressions/coreclr/GitHub_132581/CMakeLists.txt	Builds/installs the native helper library on macOS only.

Clarify why the test is RequiresProcessIsolation. Add more descriptive method / class names to test code.

jtschuster · 2026-08-31T16:59:13Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2026-08-31T16:59:24Z

Azure Pipelines: Successfully started running 1 pipeline(s).

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Review details

Files reviewed: 6/6 changed files
Comments generated: 0 new
Review effort level: Lite

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

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Review effort level: Lite

jtschuster · 2026-09-03T16:03:08Z

/ba-g Failures are an unrelated QUIC failure and #132947

jtschuster · 2026-09-03T16:04:19Z

/backport to release/11.0-rc1

github-actions · 2026-09-03T16:04:28Z

Started backporting to release/11.0-rc1 (link to workflow run)

jtschuster · 2026-09-03T16:08:12Z

/backport to release/10.0

github-actions · 2026-09-03T16:08:42Z

Started backporting to release/10.0 (link to workflow run)

@jtschuster

…signal handler (#133177) Backport of #132900 to release/10.0 /cc @jtschuster ## Customer Impact - [X] Customer reported - [ ] Found internally macOS doesn't clear sa_flags when calling execve. When dotnet is started from a process that sets a signal handler, the handler is cleared, but not the sa_flags. When the runtime gets a signal from an external source, it sees a stale SA_SIGINGO and tries to call the previous signal handler, but the pointer is set to SIG_IGN or SIG_DFL, which causes a segmentation fault and crashes the process. This change checks for those values before calling the previous signal handler. Also adds a regression test for the issue. ## Regression - [ ] Yes - [X] No ## Testing The issue was reproduced in a regression test that was added to coreclr tests. The test fails without the fix and passes with it. ## Risk Low. The actual source change is small and targeted. Co-authored-by: Jackson Schuster <36744439+jtschuster@users.noreply.github.com> Co-authored-by: Jan Kotas <jkotas@microsoft.com>

jtschuster added this to the 11.0.0 milestone Aug 28, 2026

jtschuster self-assigned this Aug 28, 2026

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build-analysis Bot mentioned this pull request Aug 28, 2026

Test Failure: System.Net.WebSockets.Client.Tests.CancelTest_SharedHandler_Loopback.ConnectAsync_Cancel_ThrowsCancellationException #130439

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elinor-fung reviewed Aug 28, 2026

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Comment thread src/tests/Regressions/coreclr/GitHub_132581/test132581.csproj

Address PR feedback

96802a1

Clarify why the test is RequiresProcessIsolation. Add more descriptive method / class names to test code.

Copilot AI review requested due to automatic review settings August 31, 2026 16:54

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Comment thread src/tests/Regressions/coreclr/GitHub_132581/test132581.csproj Outdated

Update src/tests/Regressions/coreclr/GitHub_132581/test132581.csproj

765d347

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

Copilot AI review requested due to automatic review settings September 1, 2026 19:21

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build-analysis Bot mentioned this pull request Sep 2, 2026

[ci-scan] Test failure: COM Dynamic finalizer double-unadvises connection point #132947

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jtschuster requested review from elinor-fung, jkoritzinsky and jkotas September 2, 2026 18:04

jkotas approved these changes Sep 3, 2026

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jtschuster enabled auto-merge (squash) September 3, 2026 16:01

jtschuster disabled auto-merge September 3, 2026 16:03

jtschuster merged commit 685a287 into dotnet:main Sep 3, 2026
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github-actions Bot mentioned this pull request Sep 3, 2026

[release/11.0] Check for SIG_IGN and SIG_DFL before calling previous signal handler #133176

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github-actions Bot mentioned this pull request Sep 3, 2026

[release/10.0] Check for SIG_IGN and SIG_DFL before calling previous signal handler #133177

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dotnet-maestro Bot mentioned this pull request Sep 4, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#9046

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Copilot AI mentioned this pull request Sep 5, 2026

[WIP] Fix exit code 137 in pal_sxs test #133284

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