multi: forbid curl_easy_pause from within multi socket callback#22179
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bagder wants to merge 9 commits into
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multi: forbid curl_easy_pause from within multi socket callback#22179bagder wants to merge 9 commits into
bagder wants to merge 9 commits into
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- there is a risk for a nasty recursive situation - we avoid certain risks that the pause call changes things so that when returning from the callback, the state of certain internals is undefined and we need to reload which is easy to miss - we can't think of legitiate use cases for doing this. This is basically just the new favorite point for AI and security researchers to find hypothetical problems
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Pull request overview
This PR tightens libcurl’s multi-socket callback re-entrancy rules by explicitly disallowing curl_easy_pause() from being called inside the CURLMOPT_SOCKETFUNCTION callback, aiming to avoid recursive re-entry and internal state invalidation.
Changes:
- Introduces a 3-state
in_callbacktracking value onCurl_multi(including a “forbid easy_pause” state). - Wraps multi socket callback invocations with a state that forbids
curl_easy_pause(). - Updates
curl_easy_pause(3)documentation to note the socket-callback exception.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.
Show a summary per file
| File | Description |
|---|---|
| lib/multiif.h | Changes Curl_is_in_callback() to return a multi-state value (uint8_t). |
| lib/multihandle.h | Adds callback-state constants and changes Curl_multi to store in_callback as uint8_t. |
| lib/multi.c | Implements the new multi-state callback tracking getter/setter behavior. |
| lib/multi_ev.c | Marks socket callback execution as a context that forbids curl_easy_pause(). |
| lib/easy.c | Makes curl_easy_pause() reject calls made from the forbidden socket-callback context. |
| docs/libcurl/curl_easy_pause.md | Documents the new restriction for socket callbacks. |
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Jun 26, 2026
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there is a risk for a nasty recursive situation
we avoid certain risks that the pause call changes things so that when returning from the callback, the state of certain internals is undefined and we need to reload which is easy to miss
we can't think of legitimate use cases for doing this. This is basically just the new favorite point for AI and security researchers to find hypothetical problems