SyscallSet: add ValidOnly

sandbox/linux/seccomp-bpf/syscall_iterator.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sandbox/linux/seccomp-bpf/syscall_iterator.h"
 
 #include "base/logging.h"
 #include "base/macros.h"
 #include "sandbox/linux/seccomp-bpf/linux_seccomp.h"
 
@@ skipping 21 matching lines @@
     {MIN_SYSCALL, MAX_PUBLIC_SYSCALL},
 #if defined(__arm__)
     // ARM EABI includes "ARM private" system calls starting at
     // MIN_PRIVATE_SYSCALL, and a "ghost syscall private to the kernel" at
     // MIN_GHOST_SYSCALL.
     {MIN_PRIVATE_SYSCALL, MAX_PRIVATE_SYSCALL},
     {MIN_GHOST_SYSCALL, MAX_SYSCALL},
 #endif
 };
 
-// NextSyscall returns the next system call in the specified system
-// call set after |cur|, or 0 if no such system call exists.
-uint32_t NextSyscall(uint32_t cur, bool invalid_only) {
-  for (const SyscallRange& range : kValidSyscallRanges) {
-    if (range.first > 0 && cur < range.first - 1) {
-      return range.first - 1;
-    }
-    if (cur <= range.last) {
-      if (invalid_only) {
-        return range.last + 1;
-      }
-      return cur + 1;
-    }
-  }
-
-  // BPF programs only ever operate on unsigned quantities. So, that's how
-  // we iterate; we return values from 0..0xFFFFFFFFu. But there are places,
-  // where the kernel might interpret system call numbers as signed
-  // quantities, so the boundaries between signed and unsigned values are
-  // potential problem cases. We want to explicitly return these values from
-  // our iterator.
-  if (cur < 0x7FFFFFFFu)
-    return 0x7FFFFFFFu;
-  if (cur < 0x80000000u)
-    return 0x80000000u;
-
-  if (cur < 0xFFFFFFFFu)
-    return 0xFFFFFFFFu;
-  return 0;
-}
-
 }  // namespace
 
 SyscallSet::Iterator SyscallSet::begin() const {
   return Iterator(set_, false);
 }
 
 SyscallSet::Iterator SyscallSet::end() const {
   return Iterator(set_, true);
 }
 
 bool SyscallSet::IsValid(uint32_t num) {
   for (const SyscallRange& range : kValidSyscallRanges) {
     if (num >= range.first && num <= range.last) {
       return true;
     }
   }
   return false;
 }
 
 bool operator==(const SyscallSet& lhs, const SyscallSet& rhs) {
   return (lhs.set_ == rhs.set_);
 }
 
 SyscallSet::Iterator::Iterator(Set set, bool done)
     : set_(set), done_(done), num_(0) {
-  if (set_ == Set::INVALID_ONLY && !done_ && IsValid(num_)) {
+  if (!done && set_ == (IsValid(num_) ? Set::INVALID_ONLY : Set::VALID_ONLY)) {
     ++*this;

[rickyz (no longer on Chrome), 2014/10/24 20:17:16]

This took me a little bit to wrap my head around - might be good to have a
comment like:

// Skip to the first syscall in the requested set.

[mdempsky, 2014/10/24 21:49:56]

Done.

   }
 }
 
 uint32_t SyscallSet::Iterator::operator*() const {
   DCHECK(!done_);
   return num_;
 }
 
 SyscallSet::Iterator& SyscallSet::Iterator::operator++() {
   DCHECK(!done_);
 
-  num_ = NextSyscall(num_, set_ == Set::INVALID_ONLY);
+  num_ = NextSyscall();
   if (num_ == 0) {
     done_ = true;
   }
 
   return *this;
 }
 
+// NextSyscall returns the next system call in the iterated system
+// call set after |num_|, or 0 if no such system call exists.
+uint32_t SyscallSet::Iterator::NextSyscall() const {
+  const bool want_valid = (set_ != Set::INVALID_ONLY);
+  const bool want_invalid = (set_ != Set::VALID_ONLY);
+
+  for (const SyscallRange& range : kValidSyscallRanges) {
+    if (want_invalid && range.first > 0 && num_ < range.first - 1) {

[rickyz (no longer on Chrome), 2014/10/24 20:17:17]

Might be good to comment that we're intentionally skipping over most of the
invalid range here - I was a little confused until I saw the comment in the
header.

[mdempsky, 2014/10/24 21:49:56]

Done.

+      return range.first - 1;
+    }
+    if (want_valid && num_ < range.first) {
+      return range.first;
+    }
+    if (want_valid && num_ < range.last) {
+      return num_ + 1;
+    }
+    if (want_invalid && num_ <= range.last) {
+      return range.last + 1;
+    }
+  }
+
+  if (want_invalid) {
+    // BPF programs only ever operate on unsigned quantities. So,
+    // that's how we iterate; we return values from
+    // 0..0xFFFFFFFFu. But there are places, where the kernel might
+    // interpret system call numbers as signed quantities, so the
+    // boundaries between signed and unsigned values are potential
+    // problem cases. We want to explicitly return these values from
+    // our iterator.
+    if (num_ < 0x7FFFFFFFu)
+      return 0x7FFFFFFFu;
+    if (num_ < 0x80000000u)
+      return 0x80000000u;
+
+    if (num_ < 0xFFFFFFFFu)
+      return 0xFFFFFFFFu;
+  }
+
+  return 0;
+}
+
 bool operator==(const SyscallSet::Iterator& lhs,
                 const SyscallSet::Iterator& rhs) {
   DCHECK(lhs.set_ == rhs.set_);
   return (lhs.done_ == rhs.done_) && (lhs.num_ == rhs.num_);
 }
 
 bool operator!=(const SyscallSet::Iterator& lhs,
                 const SyscallSet::Iterator& rhs) {
   return !(lhs == rhs);
 }
 
 }  // namespace sandbox