Kong / ngx_wasm_module / 9944578975

95%

Build Type

push

github

Committed by thibaultcha

Commit Message

fix(*) resolve a potential memleak in Lua bridge resolver

An occasional memory leak of Proxy-Wasm dispatch with Lua bridge
resolver, spotted by CI:

https://github.com/Kong/ngx_wasm_module/actions/runs/9884094484/job/27299927250

    ==19824== 224 bytes in 1 blocks are definitely lost in loss record 13 of 33
    ==19824==    at 0x4848899: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
    ==19824==    by 0x1E56AA: ngx_alloc (ngx_alloc.c:22)
    ==19824==    by 0x1CF926: ngx_resolver_alloc (ngx_resolver.c:4400)
    ==19824==    by 0x1CF926: ngx_resolver_calloc.isra.0 (ngx_resolver.c:4413)
    ==19824==    by 0x1D1EFD: ngx_resolve_start (ngx_resolver.c:661)
    ==19824==    by 0x392C80: ngx_wasm_socket_tcp_connect (ngx_wasm_socket_tcp.c:360)
    ==19824==    by 0x3BC984: ngx_http_proxy_wasm_dispatch_resume_handler (ngx_http_proxy_wasm_dispatch.c:745)
    ==19824==    by 0x3BD4C3: ngx_http_proxy_wasm_dispatch_handler (ngx_http_proxy_wasm_dispatch.c:477)
    ==19824==    by 0x1DFBE9: ngx_event_process_posted (ngx_event_posted.c:35)
    ==19824==    by 0x1DF0E6: ngx_process_events_and_timers (ngx_event.c:273)
    ==19824==    by 0x1EE697: ngx_single_process_cycle (ngx_process_cycle.c:323)
    ==19824==    by 0x1A9078: main (nginx.c:384)

This was caused by having 2 parallel dispatch calls using
`pwm_lua_resolver` DNS resolution. When the first call responds and
produces a downstream response, it causes pending calls to be cancelled.

However when a cancelled call had not yet finished the Lua-bridge DNS
resolution, its associated `rslv_ctx` was never freed.

This adds a "cancel" feature to Lua bridge threads, which is invoked by
TCP sockets when they are closed while having a pending Lua resolver
thread.

Run Details

42 of 44 new or added lines in 4 files covered. (95.45%)

1 existing line in 1 file now uncovered.

8737 of 9572 relevant lines covered (91.28%)

81033.24 hits per line