Merge #32 `Fix for systems with page size larger than 4k`
Tom Callaway
2 years ago
commit
fc64fd023d
@ -0,0 +1,86 @@
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From 96ee2a8e20bb7a7c4fb19e27dc31ff5c6a472849 Mon Sep 17 00:00:00 2001
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From: Ryan Gonzalez <rymg19@gmail.com>
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Date: Mon, 06 Mar 2023 20:22:25 -0600
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Subject: [PATCH] AddressTrackerLinux: Increase the message buffer size
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On non-4k-page systems, the message sizes may be too large to fit into
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the buffer, resulting in MSG_TRUNC. Instead of using the fixed 4kb size,
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follow the kernel documentation guidelines as to how large the buffer
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should be.
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Originally found by Asahi Lina:
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https://vt.social/@lina/109976892758680822
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Bug: None
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Change-Id: I4790435190167a706fa7490ab57706db1f4a6120
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---
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diff --git a/net/base/address_tracker_linux.cc b/net/base/address_tracker_linux.cc
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index 4976cae..f1a1fff 100644
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--- a/net/base/address_tracker_linux.cc
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+++ b/net/base/address_tracker_linux.cc
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@@ -14,6 +14,7 @@
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#include "base/files/scoped_file.h"
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#include "base/functional/callback_helpers.h"
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#include "base/logging.h"
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+#include "base/memory/page_size.h"
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#include "base/posix/eintr_wrapper.h"
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#include "base/task/current_thread.h"
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#include "base/threading/scoped_blocking_call.h"
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@@ -323,8 +324,30 @@
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*address_changed = false;
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*link_changed = false;
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*tunnel_changed = false;
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- char buffer[4096];
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bool first_loop = true;
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+
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+ // Varying sources have different opinions regarding the buffer size needed
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+ // for netlink messages to avoid truncation:
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+ // - The official documentation on netlink says messages are generally 8kb
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+ // or the system page size, whichever is *larger*:
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+ // https://www.kernel.org/doc/html/v6.2/userspace-api/netlink/intro.html#buffer-sizing
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+ // - The kernel headers would imply that messages are generally the system
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+ // page size or 8kb, whichever is *smaller*:
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+ // https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/include/linux/netlink.h?h=v6.2.2#n226
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+ // (libmnl follows this.)
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+ // - The netlink(7) man page's example always uses a fixed size 8kb buffer:
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+ // https://man7.org/linux/man-pages/man7/netlink.7.html
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+ // Here, we follow the guidelines in the documentation, for two primary
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+ // reasons:
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+ // - Erring on the side of a larger size is the safer way to go to avoid
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+ // MSG_TRUNC.
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+ // - Since this is heap-allocated anyway, there's no risk to the stack by
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+ // using the larger size.
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+
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+ constexpr size_t kMinNetlinkBufferSize = 8 * 1024;
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+ std::vector<char> buffer(
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+ std::max(base::GetPageSize(), kMinNetlinkBufferSize));
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+
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{
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absl::optional<base::ScopedBlockingCall> blocking_call;
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if (tracking_) {
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@@ -334,9 +357,10 @@
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}
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for (;;) {
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- int rv = HANDLE_EINTR(recv(netlink_fd_.get(), buffer, sizeof(buffer),
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- // Block the first time through loop.
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- first_loop ? 0 : MSG_DONTWAIT));
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+ int rv =
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+ HANDLE_EINTR(recv(netlink_fd_.get(), buffer.data(), buffer.size(),
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+ // Block the first time through loop.
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+ first_loop ? 0 : MSG_DONTWAIT));
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first_loop = false;
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if (rv == 0) {
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LOG(ERROR) << "Unexpected shutdown of NETLINK socket.";
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@@ -348,7 +372,8 @@
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PLOG(ERROR) << "Failed to recv from netlink socket";
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return;
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}
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- HandleMessage(buffer, rv, address_changed, link_changed, tunnel_changed);
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+ HandleMessage(buffer.data(), rv, address_changed, link_changed,
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+ tunnel_changed);
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}
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}
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if (*link_changed || *address_changed)
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