Abseil Common Libraries (C++) (grcp 依赖)
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106 lines
3.3 KiB
106 lines
3.3 KiB
// Copyright 2017 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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// base::AddressIsReadable() probes an address to see whether it is readable, |
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// without faulting. |
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#include "absl/debugging/internal/address_is_readable.h" |
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#if !defined(__linux__) || defined(__ANDROID__) |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace debugging_internal { |
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// On platforms other than Linux, just return true. |
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bool AddressIsReadable(const void* /* addr */) { return true; } |
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} // namespace debugging_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl |
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#else |
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#include <fcntl.h> |
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#include <sys/stat.h> |
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#include <sys/syscall.h> |
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#include <sys/types.h> |
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#include <unistd.h> |
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#include <cerrno> |
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#include "absl/base/internal/errno_saver.h" |
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#include "absl/base/internal/raw_logging.h" |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace debugging_internal { |
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bool AddressIsReadable(const void *addr) { |
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int fd = 0; |
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absl::base_internal::ErrnoSaver errno_saver; |
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for (int j = 0; j < 2; j++) { |
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// Here we probe with some syscall which |
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// - accepts a one-byte region of user memory as input |
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// - tests for EFAULT before other validation |
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// - has no problematic side-effects |
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// |
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// connect(2) works for this. It copies the address into kernel |
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// memory before any validation beyond requiring an open fd. |
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// But a one byte address is never valid (sa_family is two bytes), |
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// so the call cannot succeed and change any state. |
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// |
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// This strategy depends on Linux implementation details, |
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// so we rely on the test to alert us if it stops working. |
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// |
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// Some discarded past approaches: |
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// - msync() doesn't reject PROT_NONE regions |
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// - write() on /dev/null doesn't return EFAULT |
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// - write() on a pipe requires creating it and draining the writes |
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// |
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// Use syscall(SYS_connect, ...) instead of connect() to prevent ASAN |
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// and other checkers from complaining about accesses to arbitrary memory. |
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do { |
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ABSL_RAW_CHECK(syscall(SYS_connect, fd, addr, 1) == -1, |
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"should never succeed"); |
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} while (errno == EINTR); |
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if (errno == EFAULT) return false; |
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if (errno == EBADF) { |
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if (j != 0) { |
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// Unclear what happened. |
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ABSL_RAW_LOG(ERROR, "unexpected EBADF on fd %d", fd); |
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return false; |
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} |
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// fd 0 must have been closed. Try opening it again. |
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// Note: we shouldn't leak too many file descriptors here, since we expect |
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// to get fd==0 reopened. |
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fd = open("/dev/null", O_RDONLY); |
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if (fd == -1) { |
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ABSL_RAW_LOG(ERROR, "can't open /dev/null"); |
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return false; |
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} |
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} else { |
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// probably EINVAL or ENOTSOCK; we got past EFAULT validation. |
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return true; |
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} |
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} |
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ABSL_RAW_CHECK(false, "unreachable"); |
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return false; |
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} |
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} // namespace debugging_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl |
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#endif
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