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cpp/ql/src/experimental/Security/CWE/CWE-243/IncorrectChangingWorkingDirectory.cpp

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+...
+  chroot("/myFold/myTmp"); // BAD
+...
+  chdir("/myFold/myTmp"); // BAD
+...
+  int fd = open("/myFold/myTmp", O_RDONLY | O_DIRECTORY);
+  fchdir(fd); // BAD
+...
+  if (chdir("/myFold/myTmp") == -1) {
+    exit(-1);
+  }
+  if (chroot("/myFold/myTmp") == -1) {  // GOOD
+    exit(-1);
+  }
+...
+  if (chdir("/myFold/myTmp") == -1) { // GOOD
+    exit(-1);
+  }
+...
+  int fd = open("/myFold/myTmp", O_RDONLY | O_DIRECTORY);
+  if(fchdir(fd) == -1) { // GOOD
+    exit(-1);
+  }
+...

cpp/ql/src/experimental/Security/CWE/CWE-243/IncorrectChangingWorkingDirectory.qhelp

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+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+<overview>
+<p>Working with changing directories, without checking the return value or pinning the directory, may not be safe. Requires the attention of developers.</p>
+
+</recommendation>
+<example>
+<p>The following example demonstrates erroneous and corrected work with changing working directories.</p>
+<sample src="IncorrectChangingWorkingDirectory.cpp" />
+
+</example>
+<references>
+
+<li>
+  CERT C Coding Standard:
+  <a href="https://wiki.sei.cmu.edu/confluence/display/c/POS05-C.+Limit+access+to+files+by+creating+a+jail">POS05-C. Limit access to files by creating a jail</a>.
+</li>
+
+</references>
+</qhelp>

cpp/ql/src/experimental/Security/CWE/CWE-243/IncorrectChangingWorkingDirectory.ql

@@ -0,0 +1,70 @@
+/**
+ * @name Find work with changing working directories, with security errors.
+ * @description Not validating the return value or pinning the directory can be unsafe.
+ * @kind problem
+ * @id cpp/work-with-changing-working-directories
+ * @problem.severity warning
+ * @precision medium
+ * @tags correctness
+ *       security
+ *       external/cwe/cwe-243
+ *       external/cwe/cwe-252
+ */
+
+import cpp
+
+/** Holds if a `fc` function call is available before or before a `chdir` function call. */
+predicate inExistsChdir(FunctionCall fcp) {
+  exists(FunctionCall fctmp |
+    (
+      fctmp.getTarget().hasGlobalOrStdName("chdir") or
+      fctmp.getTarget().hasGlobalOrStdName("fchdir")
+    ) and
+    (
+      fctmp.getASuccessor*() = fcp or
+      fcp.getASuccessor*() = fctmp
+    )
+  )
+}
+
+/** Holds if a `fc` function call is available before or before a function call containing a `chdir` call. */
+predicate outExistsChdir(FunctionCall fcp) {
+  exists(FunctionCall fctmp |
+    exists(FunctionCall fctmp2 |
+      (
+        fctmp2.getTarget().hasGlobalOrStdName("chdir") or
+        fctmp2.getTarget().hasGlobalOrStdName("fchdir")
+      ) and
+      fctmp2.getEnclosingStmt().getParentStmt*() = fctmp.getTarget().getEntryPoint().getChildStmt*()
+    ) and
+    (
+      fctmp.getASuccessor*() = fcp or
+      fcp.getASuccessor*() = fctmp
+    )
+  )
+}
+
+from FunctionCall fc, string msg
+where
+  fc.getTarget().hasGlobalOrStdName("chroot") and
+  not inExistsChdir(fc) and
+  not outExistsChdir(fc) and
+  exists(FunctionCall fctmp |
+    fc.getEnclosingStmt().getParentStmt*() = fctmp.getTarget().getEntryPoint().getChildStmt*() and
+    not inExistsChdir(fctmp) and
+    not outExistsChdir(fctmp)
+  ) and
+  msg = "Creation of chroot Jail Without Changing Working Directory out"
+  or
+  (
+    fc.getTarget().hasGlobalOrStdName("chdir") or
+    fc.getTarget().hasGlobalOrStdName("fchdir")
+  ) and
+  not exists(ConditionalStmt cotmp | cotmp.getControllingExpr().getAChild*() = fc) and
+  not exists(Loop lptmp | lptmp.getCondition().getAChild*() = fc) and
+  not exists(ReturnStmt rttmp | rttmp.getExpr().getAChild*() = fc) and
+  not exists(Assignment astmp | astmp.getAChild*() = fc) and
+  not exists(Initializer ittmp | ittmp.getExpr().getAChild*() = fc) and
+  not fc.isInMacroExpansion() and
+  msg = fc.getTarget().getName() + " unchecked return value."
+select fc, msg