[PR #6848] [client] Fix nil context panic in iOS dynamic route resolver #27290

New Issue

saavagebueno · 2026-08-05T07:08:30-04:00

saavagebueno commented

2026-08-05 07:08:30 -04:00

Original Pull Request: https://github.com/netbirdio/netbird/pull/6848

State: closed
Merged: Yes

Describe your changes

getIPsFromResolver passed a nil context to ExchangeWithFallback, which net.Dialer.DialContext rejects with panic("nil context"). On iOS this crashed the whole network extension (SIGABRT) ~2 seconds after connect whenever the network map contained a domain-based (dynamic) route, as the resolver goroutine panicked on its first DNS query.

Passing nil used to be a documented input of ExchangeWithFallback ("If the passed context is nil, this will use Exchange instead of ExchangeContext") since #3632. 9ed2e2a5b (#5971) removed the nil-context branch, but this iOS-only caller was not updated — it never fails CI since route_ios.go only builds with GOOS=ios. Broken since v0.71.1.

Pass a context bounded by the existing dialTimeout instead, matching the dnsinterceptor pattern (context.Background() + timeout).

Captured panic (netbird.err):
panic: nil context
net.(*Dialer).DialContext -> miekg/dns ExchangeContext ->
nbdns.ExchangeWithFallback(nil, ...) -> dynamic.(*Route).getIPsFromResolver
route_ios.go:35

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Is a feature enhancement
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Created tests that fail without the change (if possible)
This change does not modify the public API, gRPC protocols, functionality behavior, CLI / service flags, or introduce a new feature — OR I have discussed it with the NetBird team beforehand (link the issue / Slack thread in the description). See CONTRIBUTING.md.

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Summary by CodeRabbit

Bug Fixes
- Fixed iOS dynamic DNS resolution by ensuring DNS queries use a proper resolver context instead of a nil one.
- Improved DNS resolution reliability by propagating cancellation/timeouts through all domain IP lookups, including fallback system resolver queries.

**Original Pull Request:** https://github.com/netbirdio/netbird/pull/6848 **State:** closed **Merged:** Yes --- ## Describe your changes getIPsFromResolver passed a nil context to ExchangeWithFallback, which net.Dialer.DialContext rejects with panic("nil context"). On iOS this crashed the whole network extension (SIGABRT) ~2 seconds after connect whenever the network map contained a domain-based (dynamic) route, as the resolver goroutine panicked on its first DNS query. Passing nil used to be a documented input of ExchangeWithFallback ("If the passed context is nil, this will use Exchange instead of ExchangeContext") since #3632. 9ed2e2a5b (#5971) removed the nil-context branch, but this iOS-only caller was not updated — it never fails CI since route_ios.go only builds with GOOS=ios. Broken since v0.71.1. Pass a context bounded by the existing dialTimeout instead, matching the dnsinterceptor pattern (context.Background() + timeout). Captured panic (netbird.err): panic: nil context net.(*Dialer).DialContext -> miekg/dns ExchangeContext -> nbdns.ExchangeWithFallback(nil, ...) -> dynamic.(*Route).getIPsFromResolver route_ios.go:35 ## Issue ticket number and link ## Stack  ### Checklist - [x] Is it a bug fix - [ ] Is a typo/documentation fix - [ ] Is a feature enhancement - [ ] It is a refactor - [ ] Created tests that fail without the change (if possible) - [ ] This change does **not** modify the public API, gRPC protocols, functionality behavior, CLI / service flags, or introduce a new feature — **OR** I have discussed it with the NetBird team beforehand (link the issue / Slack thread in the description). See [CONTRIBUTING.md](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTING.md#discuss-changes-with-the-netbird-team-first). > By submitting this pull request, you confirm that you have read and agree to the terms of the [Contributor License Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md). ## Documentation Select exactly one: - [ ] I added/updated documentation for this change - [x] Documentation is **not needed** for this change (explain why) ### Docs PR URL (required if "docs added" is checked) Paste the PR link from https://github.com/netbirdio/docs here: https://github.com/netbirdio/docs/pull/__  --- <a href="https://app.blacksmith.sh/netbirdio/codesmith/netbird/pr/6848"><picture><source media="(prefers-color-scheme: dark)" srcset="https://pr-comments-assets.blacksmith.sh/codesmith/view-with-codesmith-dark-v2.svg"><source media="(prefers-color-scheme: light)" srcset="https://pr-comments-assets.blacksmith.sh/codesmith/view-with-codesmith-light-v2.svg"><img alt="View with Codesmith" src="https://pr-comments-assets.blacksmith.sh/codesmith/view-with-codesmith-dark-v2.svg"></picture></a> <a href="https://backend.blacksmith.sh/track/enable-autofix?expires=1787223752&installation_model_id=427504&pr_number=6848&repository=netbirdio%2Fnetbird&return_to=https%3A%2F%2Fgithub.com%2Fnetbirdio%2Fnetbird%2Fpull%2F6848&signature=881d3b30aa4bd15001562ad417ff946b70c7c108856a1b3808b776c12b7022a9"><picture><source media="(prefers-color-scheme: dark)" srcset="https://pr-comments-assets.blacksmith.sh/codesmith/autofix-with-codesmith-dark.svg"><source media="(prefers-color-scheme: light)" srcset="https://pr-comments-assets.blacksmith.sh/codesmith/autofix-with-codesmith-light.svg"><img alt="Autofix with Codesmith" src="https://pr-comments-assets.blacksmith.sh/codesmith/autofix-with-codesmith-dark.svg"></picture></a> <sup>Need help on this PR? Tag <code>/codesmith</code> with what you need. Autofix is disabled.</sup>    ## Summary by CodeRabbit * **Bug Fixes** * Fixed iOS dynamic DNS resolution by ensuring DNS queries use a proper resolver context instead of a nil one. * Improved DNS resolution reliability by propagating cancellation/timeouts through all domain IP lookups, including fallback system resolver queries.

saavagebueno added the pull-request label 2026-08-05 07:08:30 -04:00

saavagebueno closed this issue

2026-08-05 07:08:30 -04:00

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Reference: DYNR/netbird#27290