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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/187030">187030</a></dd>
<dt>Author</dt> <dd>mcatanzaro@igalia.com</dd>
<dt>Date</dt> <dd>2015-07-20 13:06:27 -0700 (Mon, 20 Jul 2015)</dd>
</dl>
<h3>Log Message</h3>
<pre>[Seccomp] Should be easier to debug blocked syscalls
https://bugs.webkit.org/show_bug.cgi?id=142980
These should be printed even when not running in debug mode. There is no
value in hiding errors from release build users.
Reviewed by Žan Doberšek.
* Shared/linux/SeccompFilters/SeccompBroker.cpp:
(WebKit::SeccompBroker::runLoop): Don't close stderr et. al. in release builds.
* Shared/linux/SeccompFilters/Syscall.cpp:
(WebKit::write_uint): Added.
(WebKit::reportUnexpectedSyscall): Added.
(WebKit::Syscall::createFromContext): Call reportUnexpectedSyscall. Also, no need to crash
here in release builds.
* Shared/linux/SeccompFilters/SyscallPolicy.cpp:
(WebKit::SyscallPolicy::hasPermissionForPath): Print a warning when access is denied.
(WebKit::SyscallPolicy::permissionToString): Added.
* Shared/linux/SeccompFilters/SyscallPolicy.h: Add permissionToString.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebKit2ChangeLog">trunk/Source/WebKit2/ChangeLog</a></li>
<li><a href="#trunkSourceWebKit2SharedlinuxSeccompFiltersSeccompBrokercpp">trunk/Source/WebKit2/Shared/linux/SeccompFilters/SeccompBroker.cpp</a></li>
<li><a href="#trunkSourceWebKit2SharedlinuxSeccompFiltersSyscallcpp">trunk/Source/WebKit2/Shared/linux/SeccompFilters/Syscall.cpp</a></li>
<li><a href="#trunkSourceWebKit2SharedlinuxSeccompFiltersSyscallPolicycpp">trunk/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.cpp</a></li>
<li><a href="#trunkSourceWebKit2SharedlinuxSeccompFiltersSyscallPolicyh">trunk/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebKit2ChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit2/ChangeLog (187029 => 187030)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit2/ChangeLog 2015-07-20 19:50:54 UTC (rev 187029)
+++ trunk/Source/WebKit2/ChangeLog 2015-07-20 20:06:27 UTC (rev 187030)
</span><span class="lines">@@ -1,3 +1,25 @@
</span><ins>+2015-07-20 Michael Catanzaro <mcatanzaro@igalia.com>
+
+ [Seccomp] Should be easier to debug blocked syscalls
+ https://bugs.webkit.org/show_bug.cgi?id=142980
+
+ These should be printed even when not running in debug mode. There is no
+ value in hiding errors from release build users.
+
+ Reviewed by Žan Doberšek.
+
+ * Shared/linux/SeccompFilters/SeccompBroker.cpp:
+ (WebKit::SeccompBroker::runLoop): Don't close stderr et. al. in release builds.
+ * Shared/linux/SeccompFilters/Syscall.cpp:
+ (WebKit::write_uint): Added.
+ (WebKit::reportUnexpectedSyscall): Added.
+ (WebKit::Syscall::createFromContext): Call reportUnexpectedSyscall. Also, no need to crash
+ here in release builds.
+ * Shared/linux/SeccompFilters/SyscallPolicy.cpp:
+ (WebKit::SyscallPolicy::hasPermissionForPath): Print a warning when access is denied.
+ (WebKit::SyscallPolicy::permissionToString): Added.
+ * Shared/linux/SeccompFilters/SyscallPolicy.h: Add permissionToString.
+
</ins><span class="cx"> 2015-07-20 Csaba Osztrogonác <ossy@webkit.org>
</span><span class="cx">
</span><span class="cx"> Fix the !ENABLE(VIDEO) build after r186396
</span></span></pre></div>
<a id="trunkSourceWebKit2SharedlinuxSeccompFiltersSeccompBrokercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit2/Shared/linux/SeccompFilters/SeccompBroker.cpp (187029 => 187030)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit2/Shared/linux/SeccompFilters/SeccompBroker.cpp 2015-07-20 19:50:54 UTC (rev 187029)
+++ trunk/Source/WebKit2/Shared/linux/SeccompFilters/SeccompBroker.cpp 2015-07-20 20:06:27 UTC (rev 187030)
</span><span class="lines">@@ -320,16 +320,11 @@
</span><span class="cx">
</span><span class="cx"> NO_RETURN void SeccompBroker::runLoop(int socket)
</span><span class="cx"> {
</span><del>-#ifndef NDEBUG
- int i = STDERR_FILENO + 1;
-#else
- int i = 0;
-#endif
- // Close all inherited file descriptors other
- // than the socket to the sandboxed process.
- for (; i < FD_SETSIZE; ++i)
</del><ins>+ // Close unnecessary inherited file descriptors.
+ for (int i = STDERR_FILENO + 1; i < FD_SETSIZE; ++i) {
</ins><span class="cx"> if (i != socket)
</span><span class="cx"> close(i);
</span><ins>+ }
</ins><span class="cx">
</span><span class="cx"> while (true) {
</span><span class="cx"> char buffer[messageMaxSize];
</span></span></pre></div>
<a id="trunkSourceWebKit2SharedlinuxSeccompFiltersSyscallcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit2/Shared/linux/SeccompFilters/Syscall.cpp (187029 => 187030)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit2/Shared/linux/SeccompFilters/Syscall.cpp 2015-07-20 19:50:54 UTC (rev 187029)
+++ trunk/Source/WebKit2/Shared/linux/SeccompFilters/Syscall.cpp 2015-07-20 20:06:27 UTC (rev 187030)
</span><span class="lines">@@ -1,5 +1,6 @@
</span><span class="cx"> /*
</span><span class="cx"> * Copyright (C) 2013 Intel Corporation. All rights reserved.
</span><ins>+ * Copyright (C) 2015 Igalia S.L.
</ins><span class="cx"> *
</span><span class="cx"> * Redistribution and use in source and binary forms, with or without
</span><span class="cx"> * modification, are permitted provided that the following conditions
</span><span class="lines">@@ -32,10 +33,47 @@
</span><span class="cx"> #include "OpenSyscall.h"
</span><span class="cx"> #include "SigactionSyscall.h"
</span><span class="cx"> #include "SigprocmaskSyscall.h"
</span><ins>+#include <limits>
</ins><span class="cx"> #include <seccomp.h>
</span><ins>+#include <string.h>
+#include <unistd.h>
</ins><span class="cx">
</span><span class="cx"> namespace WebKit {
</span><span class="cx">
</span><ins>+// The redundant "constexpr const" is to placate Clang's -Wwritable-strings.
+static constexpr const char* const message = "Blocked unexpected syscall: ";
+
+// Since "sprintf" is not signal-safe, reimplement %d here. Based on code from
+// http://outflux.net/teach-seccomp by Will Drewry and Kees Cook, released under
+// the Chromium BSD license.
+static void writeUnsignedInt(char* buf, unsigned val)
+{
+ int width = 0;
+ unsigned tens;
+
+ if (!val) {
+ strcpy(buf, "0");
+ return;
+ }
+ for (tens = val; tens; tens /= 10)
+ ++width;
+ buf[width] = '\0';
+ for (tens = val; tens; tens /= 10)
+ buf[--width] = '0' + (tens % 10);
+}
+
+static void reportUnexpectedSyscall(int syscall)
+{
+ char buf[128];
+#if defined(__has_builtin) && __has_builtin(__builtin_strlen)
+ static_assert(__builtin_strlen(message) + std::numeric_limits<int>::digits10 + 1 < sizeof(buf), "Buffer too small");
+#endif
+ strcpy(buf, message);
+ writeUnsignedInt(buf + strlen(buf), syscall);
+ strcat(buf, "\n");
+ write(STDERR_FILENO, buf, strlen(buf));
+}
+
</ins><span class="cx"> std::unique_ptr<Syscall> Syscall::createFromContext(ucontext_t* ucontext)
</span><span class="cx"> {
</span><span class="cx"> mcontext_t* mcontext = &ucontext->uc_mcontext;
</span><span class="lines">@@ -54,7 +92,8 @@
</span><span class="cx"> case __NR_rt_sigaction:
</span><span class="cx"> return SigactionSyscall::createFromContext(mcontext);
</span><span class="cx"> default:
</span><del>- CRASH();
</del><ins>+ reportUnexpectedSyscall(mcontext->gregs[REG_SYSCALL]);
+ ASSERT_NOT_REACHED();
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> return nullptr;
</span></span></pre></div>
<a id="trunkSourceWebKit2SharedlinuxSeccompFiltersSyscallPolicycpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.cpp (187029 => 187030)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.cpp 2015-07-20 19:50:54 UTC (rev 187029)
+++ trunk/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.cpp 2015-07-20 20:06:27 UTC (rev 187030)
</span><span class="lines">@@ -97,7 +97,13 @@
</span><span class="cx"> free(basePath);
</span><span class="cx"> free(canonicalPath);
</span><span class="cx">
</span><del>- return (permission & policy->value) == permission;
</del><ins>+ if ((permission & policy->value) == permission)
+ return true;
+
+ // Don't warn if the file doesn't exist at all.
+ if (!access(path, F_OK) || errno != ENOENT)
+ fprintf(stderr, "Blocked impermissible %s access to %s\n", SyscallPolicy::permissionToString(permission), path);
+ return false;
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void SyscallPolicy::addFilePermission(const String& path, Permission permission)
</span><span class="lines">@@ -256,6 +262,23 @@
</span><span class="cx"> #endif
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+const char* SyscallPolicy::permissionToString(Permission permission)
+{
+ switch (permission) {
+ case Read:
+ return "read";
+ case Write:
+ return "write";
+ case ReadAndWrite:
+ return "read/write";
+ case NotAllowed:
+ return "disallowed";
+ }
+
+ ASSERT_NOT_REACHED();
+ return "unknown action";
+}
+
</ins><span class="cx"> } // namespace WebKit
</span><span class="cx">
</span><span class="cx"> #endif // ENABLE(SECCOMP_FILTERS)
</span></span></pre></div>
<a id="trunkSourceWebKit2SharedlinuxSeccompFiltersSyscallPolicyh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.h (187029 => 187030)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.h 2015-07-20 19:50:54 UTC (rev 187029)
+++ trunk/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.h 2015-07-20 20:06:27 UTC (rev 187030)
</span><span class="lines">@@ -52,6 +52,8 @@
</span><span class="cx">
</span><span class="cx"> void addDefaultWebProcessPolicy(const WebProcessCreationParameters&);
</span><span class="cx">
</span><ins>+ static const char* permissionToString(Permission);
+
</ins><span class="cx"> private:
</span><span class="cx"> typedef HashMap<String, int> PermissionMap;
</span><span class="cx"> PermissionMap m_filePermission;
</span></span></pre>
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