Attachment 249264 Details for Bug 142980 – [Linux] Seccomp Filters: Make it easier to debug blocked syscalls

[patch] [Linux] Seccomp Filters: Make it easier to debug blocked syscalls

bug-142980-20150323155353.patch (text/plain), 8.27 KB, created by Michael Catanzaro on 2015-03-23 13:54:30 PDT

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Creator: Michael Catanzaro

Created: 2015-03-23 13:54:30 PDT

Size: 8.27 KB

patch

obsolete

>Subversion Revision: 181825
>diff --git a/Source/WebKit2/ChangeLog b/Source/WebKit2/ChangeLog
>index b0cac22e3e0ce409ab73e71056f185f220a36a71..471ac892e51b5ee0c86ba8446880aea313eb13f9 100644
>--- a/Source/WebKit2/ChangeLog
>+++ b/Source/WebKit2/ChangeLog
>@@ -1,3 +1,26 @@
>+2015-03-23  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. Also, I don't have the
>+        patience to use a debug build for development.
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        * 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.
>+
> 2015-01-04  Michael Catanzaro  <mcatanzaro@igalia.com>
> 
>         [GTK] Add seccomp filters support
>diff --git a/Source/WebKit2/Shared/linux/SeccompFilters/SeccompBroker.cpp b/Source/WebKit2/Shared/linux/SeccompFilters/SeccompBroker.cpp
>index 1ca63ffdb7fa75c5b987d87b9d446b0e3cc859f3..234e3827fa89bcd7b80b19b2feb085380d2296b1 100644
>--- a/Source/WebKit2/Shared/linux/SeccompFilters/SeccompBroker.cpp
>+++ b/Source/WebKit2/Shared/linux/SeccompFilters/SeccompBroker.cpp
>@@ -320,14 +320,8 @@ void SeccompBroker::initialize()
> 
> NO_RETURN void SeccompBroker::runLoop(int socket)
> {
>-#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)
>+    // Close unnecessary inherited file descriptors.
>+    for (int i = STDERR_FILENO + 1; i < FD_SETSIZE; ++i)
>         if (i != socket)
>             close(i);
> 
>diff --git a/Source/WebKit2/Shared/linux/SeccompFilters/Syscall.cpp b/Source/WebKit2/Shared/linux/SeccompFilters/Syscall.cpp
>index 0d4afd0dd22309d90ebefa3ee67b46138334a5e7..ca08bbfcfd43e0f899e16e15b7f359e5b29ab831 100644
>--- a/Source/WebKit2/Shared/linux/SeccompFilters/Syscall.cpp
>+++ b/Source/WebKit2/Shared/linux/SeccompFilters/Syscall.cpp
>@@ -1,5 +1,6 @@
> /*
>  * Copyright (C) 2013 Intel Corporation. All rights reserved.
>+ * Copyright (C) 2015 Igalia S.L.
>  *
>  * Redistribution and use in source and binary forms, with or without
>  * modification, are permitted provided that the following conditions
>@@ -23,6 +24,41 @@
>  * THE POSSIBILITY OF SUCH DAMAGE.
>  */
> 
>+/*
>+ * Safe printing based on code from http://outflux.net/teach-seccomp
>+ *
>+ * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
>+ * Authors:
>+ *  Will Drewry <wad@chromium.org>
>+ *  Kees Cook <keescook@chromium.org>
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions are
>+ * met:
>+ *
>+ *  * Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ *  * Redistributions in binary form must reproduce the above
>+ *    copyright notice, this list of conditions and the following disclaimer
>+ *    in the documentation and/or other materials provided with the
>+ *    distribution.
>+ *  * Neither the name of Google Inc. nor the names of its
>+ *    contributors may be used to endorse or promote products derived from
>+ *    this software without specific prior written permission.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
>+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
>+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
>+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
>+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
>+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
>+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
>+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
>+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
> #include "config.h"
> #include "Syscall.h"
> 
>@@ -32,10 +68,42 @@
> #include "OpenSyscall.h"
> #include "SigactionSyscall.h"
> #include "SigprocmaskSyscall.h"
>+#include <limits>
> #include <seccomp.h>
>+#include <string.h>
>+#include <unistd.h>
> 
> namespace WebKit {
> 
>+static const char* const msg_needed = "Blocked unexpected syscall: ";
>+
>+// Since "sprintf" is not signal-safe, reimplement %d here.
>+static void write_uint(char* buf, unsigned val)
>+{
>+    int width = 0;
>+    unsigned tens;
>+
>+    if (val == 0) {
>+        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];
>+    static_assert(strlen(msg_needed) + std::numeric_limits<int>::digits10 + 1 < sizeof(buf), "Buffer too small");
>+    strcpy(buf, msg_needed);
>+    write_uint(buf + strlen(buf), syscall);
>+    strcat(buf, "\n");
>+    write(STDERR_FILENO, buf, strlen(buf));
>+}
>+
> std::unique_ptr<Syscall> Syscall::createFromContext(ucontext_t* ucontext)
> {
>     mcontext_t* mcontext = &ucontext->uc_mcontext;
>@@ -54,7 +122,8 @@ std::unique_ptr<Syscall> Syscall::createFromContext(ucontext_t* ucontext)
>     case __NR_rt_sigaction:
>         return SigactionSyscall::createFromContext(mcontext);
>     default:
>-        CRASH();
>+        reportUnexpectedSyscall(mcontext->gregs[REG_SYSCALL]);
>+        ASSERT_NOT_REACHED();
>     }
> 
>     return nullptr;
>diff --git a/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.cpp b/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.cpp
>index 2d315d785bc0923a348571365f9ee439a021bee5..86d12995eca66af063f13f870e1fc57a5ad61275 100644
>--- a/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.cpp
>+++ b/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.cpp
>@@ -97,7 +97,13 @@ bool SyscallPolicy::hasPermissionForPath(const char* path, Permission permission
>     free(basePath);
>     free(canonicalPath);
> 
>-    return (permission & policy->value) == permission;
>+    if ((permission & policy->value) == permission)
>+        return true;
>+
>+    // Don't warn if the file doesn't exist at all.
>+    if (access(path, F_OK) == 0 || errno != ENOENT)
>+        fprintf(stderr, "Blocked impermissible %s access to %s\n", SyscallPolicy::permissionToString(permission), path);
>+    return false;
> }
> 
> void SyscallPolicy::addFilePermission(const String& path, Permission permission)
>@@ -256,6 +262,21 @@ void SyscallPolicy::addDefaultWebProcessPolicy(const WebProcessCreationParameter
> #endif
> }
> 
>+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";
>+    }
>+    CRASH();
>+}
>+
> } // namespace WebKit
> 
> #endif // ENABLE(SECCOMP_FILTERS)
>diff --git a/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.h b/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.h
>index cae0e45d2f8c2e77d058acbc1c7359869c622f3c..4b3886e6e90a9fc901799bf7bd6e58c54aea8f26 100644
>--- a/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.h
>+++ b/Source/WebKit2/Shared/linux/SeccompFilters/SyscallPolicy.h
>@@ -52,6 +52,8 @@ public:
> 
>     void addDefaultWebProcessPolicy(const WebProcessCreationParameters&);
> 
>+    static const char* permissionToString(Permission);
>+
> private:
>     typedef HashMap<String, int> PermissionMap;
>     PermissionMap m_filePermission;

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Attachments on bug 142980: 249264 | 249265 | 249274 | 257067 | 257114