route: Routes may not have an interface assinged

[rsmarples]

As such, we cannot access dhcpcd_ctx so we can't use the free route list.
Fixes #571.

[coderabbitai]

Walkthrough

The changes fix a NULL pointer dereference vulnerability in route cleanup code. When rt_headclear processes a route node with a NULL interface pointer, it now safely passes NULL context to rt_headclear0 instead of dereferencing the NULL pointer, and rt_headclear0 now conditionally guards its assertion against NULL contexts.

Changes

Cohort / File(s)	Summary
NULL pointer dereference fix in route cleanup src/route.c	Modified rt_headclear to check if rt->rt_ifp is NULL before dereferencing it for ctx; updated rt_headclear0 to conditionally assert ctx is non-NULL only under RT_FREE_ROUTE_TABLE when ctx is actually non-NULL

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'route: Routes may not have an interface assinged' directly addresses the core change—handling routes without an interface pointer.
Description check	✅ Passed	The description explains that routes may lack an associated interface, preventing ctx access, and references issue #571 which documents the NULL-pointer dereference.
Linked Issues check	✅ Passed	The code changes directly fix the NULL-pointer dereference in rt_headclear by guarding against NULL ctx and conditionally passing NULL ctx when rt_ifp is NULL.
Out of Scope Changes check	✅ Passed	The changes to rt_headclear0 and rt_headclear are directly focused on preventing NULL-pointer dereference and do not introduce unrelated modifications.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix-route-headclear

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📥 Commits

Reviewing files that changed from the base of the PR and between 117742d and 83eafa0.

📒 Files selected for processing (1)

• src/route.c

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• GitHub Check: netbsd (--disable-ipv6)
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🔇 Additional comments (2)

src/route.c (2)

317-318: LGTM! Properly guards assertion against NULL context.

The conditional check correctly prevents the assertion from executing when ctx is NULL, which occurs when routes lack an associated interface. Since rt_free handles NULL rt_ifp by directly freeing the route (bypassing the free route table), this assertion isn't needed in that case.

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338-338: LGTM! Correctly prevents NULL pointer dereference.

The ternary operator safely checks whether rt->rt_ifp is NULL before dereferencing it to access ctx. This directly fixes the NULL pointer dereference vulnerability reported in issue #571, where routes without an associated interface would cause a crash during cleanup.

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