v31.1-roots.1 · Commit 6: [PATCH 06/17] feat(wallet): preserve Roots signing and spend controls on v31
src/util/subprocess.cpp
Before: /dev/null · After: src/util/subprocess.cpp
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src/util/subprocess.cpp
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// Copyright (c) 2025-present The Bitcoin Roots developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include <bitcoin-build-config.h> // IWYU pragma: keep
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#ifndef WIN32
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#if HAVE_CLOSE_RANGE_LINUX
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#ifndef _GNU_SOURCE
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#define _GNU_SOURCE
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#endif
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#include <linux/close_range.h>
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#endif
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#include <cerrno>
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#include <cstddef>
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#include <cstdint>
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#include <cstring>
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#include <fcntl.h>
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#include <limits.h>
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#include <unistd.h>
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#ifdef __linux__
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#include <sys/syscall.h>
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#endif
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namespace subprocess::detail {
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#ifdef __linux__
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// The kernel ABI for getdents64. No libc directory iterator or heap storage is
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// used after fork: /proc enumerates the actual descriptors, including ones above
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// a subsequently lowered RLIMIT_NOFILE.
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struct LinuxDirent64 {
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uint64_t inode;
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int64_t offset;
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unsigned short record_length;
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unsigned char type;
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char name[1];
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};
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static bool CloseProcDescriptors() noexcept
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{
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const int directory = open("/proc/self/fd", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
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if (directory < 0) return false;
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alignas(LinuxDirent64) char buffer[4096];
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bool success{true};
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for (;;) {
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const long count = syscall(SYS_getdents64, directory, buffer, sizeof(buffer));
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if (count == 0) break;
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if (count < 0) {
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if (errno == EINTR) continue;
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success = false;
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break;
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}
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for (long position{0}; position < count;) {
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constexpr size_t name_offset{offsetof(LinuxDirent64, name)};
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if (count - position <= static_cast<long>(name_offset)) {
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success = false;
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break;
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}
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unsigned short record_length;
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std::memcpy(&record_length, buffer + position + offsetof(LinuxDirent64, record_length), sizeof(record_length));
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const char* name{buffer + position + name_offset};
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if (record_length <= name_offset || record_length > count - position) {
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success = false;
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break;
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}
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int fd{0};
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size_t digit{0};
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for (; digit < record_length - name_offset; ++digit) {
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const char ch{name[digit]};
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if (ch < '0' || ch > '9' || fd > (INT_MAX - (ch - '0')) / 10) break;
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fd = fd * 10 + ch - '0';
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}
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if (digit > 0 && digit < record_length - name_offset && name[digit] == '\0' && fd > 3 && fd != directory) close(fd);
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position += record_length;
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}
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if (!success) break;
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}
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close(directory);
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return success;
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}
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#endif
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bool subprocess_close_all_fds(int& except_fd, [[maybe_unused]] bool force_fallback) noexcept
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{
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if (except_fd < 3) return false;
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// Keep the exec-error pipe at a fixed descriptor so native close-from APIs
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// need no exception list or scan of a potentially enormous numeric range.
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if (except_fd != 3) {
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if (dup2(except_fd, 3) < 0) return false;
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close(except_fd);
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except_fd = 3;
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}
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if (fcntl(3, F_SETFD, FD_CLOEXEC) < 0) return false;
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#if HAVE_CLOSE_RANGE_GENERIC || HAVE_CLOSE_RANGE_LINUX
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if (!force_fallback && close_range(4, UINT_MAX, 0) == 0) return true;
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#endif
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#ifdef __linux__
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return CloseProcDescriptors();
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#elif HAVE_CLOSEFROM_RETURN_INT
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return closefrom(4) == 0;
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#elif HAVE_CLOSEFROM
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closefrom(4);
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return true;
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#else
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// An unsupported or unavailable safe closure mechanism must not allow the
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// signer to execute with unrelated inherited descriptors.
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return false;
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#endif
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}
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} // namespace subprocess::detail
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#endif // !WIN32
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