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DanSandClaude Opus 5.5 7131b3673f qa: add fd-guard, the close() guard and regtest harness that found the double close
shim/ is an LD_PRELOAD guard around close/fclose/dup2/dup3:
- before each close it resolves /proc/self/fd/N;
- it reports, with a backtrace, a non-owner close of wallet.dat,
  database/log.* or blocks/*.dat, and every close that fails with EBADF
  (the second half of a double close);
- FDGUARD_ABORT=1 aborts on the first hit;
- run_tests.sh self-tests it (51 checks).

repro/ runs a shimmed dragonxd on isolated regtest. Each run gets its
own unprivileged network namespace (loopback only). The loads are:
- rpc: a hammer with impatient/RST/half-open clients, work-queue
  bursts and long-polls;
- p2p: TLS peers churned by disconnectnode, ban and kill, plus a raw
  TCP/TLS misbehaver;
- tor: a fake control port;
- mine: mining with blocknotify and autoshield.
tools/tally.py groups the reports by closer. tools/scan_bdb.py finds BDB
pages written into block files.

With the wolfSSL CloseSocket macro in effect:
- p2pmin (300 s) gives one EBADF double close per disconnect;
- the full load (1200 s) gives 930 EBADF closes, 186 non-owner closes
  (37 of wallet/log/blk files) and a 632 KB db.log with BDB0060 PANIC;
- RPC-only and Tor-only loads give none.
After the fix, every count is 0 and db.log stays empty. The README has
the commands and the numbers.

Paths come from the environment (GOLDEN, BIN, RUNS, SHIM, ASMAP and the
Sapling params). Run output goes to $RUNS, outside the tree.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-16 21:23:01 -05:00

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#!/bin/sh
# Build the fdguard LD_PRELOAD shim and its self-test program.
# ./build.sh -> libfdguard.so, fdguard_test
set -e
cd "$(dirname "$0")"
CC=${CC:-gcc}
$CC -O2 -g -fPIC -shared -Wall -Wextra -Wno-unused-parameter -fvisibility=default \
-o libfdguard.so.tmp fdguard.c -ldl -lpthread
# rename, never overwrite in place: a running process may have the old one mapped
mv -f libfdguard.so.tmp libfdguard.so
# the test program keeps its symbols (no -rdynamic on purpose: like dragonxd,
# owner detection must work from .symtab alone) and frame pointers for clarity
$CC -O1 -g -fno-omit-frame-pointer -fno-inline -Wall -o fdguard_test.tmp fdguard_test.c -lpthread
mv -f fdguard_test.tmp fdguard_test
echo "built: $(pwd)/libfdguard.so $(pwd)/fdguard_test"