[Lldb-commits] [lldb] r220650 - Fix HelloWorld attach test for Linux kernels with ptrace ancestor lockdown.

Todd Fiala todd.fiala at gmail.com
Sun Oct 26 14:37:46 PDT 2014

Author: tfiala
Date: Sun Oct 26 16:37:46 2014
New Revision: 220650

URL: http://llvm.org/viewvc/llvm-project?rev=220650&view=rev
Fix HelloWorld attach test for Linux kernels with ptrace ancestor lockdown.

Similar to a recent test I fixed for gdb-remote attach scenarios, this
fix is for Linux kernels, such as Ubuntu's stock setup on 11.04-ish and
later, where ptrace starts requiring a ptracer to be an ancestor of the
inferior to be ptraced.  This change checks for Linux and the ptrace-related
flags.  If they're found, it tries to switch on the "allow any ptracer" mode
for the inferior as the first statements in the program.  It's a best-effort
solution - if the prctl call fails, the failure is ignored, and probably will
lead to the test failing.

The ptrace security behavior can be modified system-wide, but is outside the
scope of the test to address.  Hence I went with this particular solution.


Modified: lldb/trunk/test/python_api/hello_world/main.c
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/test/python_api/hello_world/main.c?rev=220650&r1=220649&r2=220650&view=diff
--- lldb/trunk/test/python_api/hello_world/main.c (original)
+++ lldb/trunk/test/python_api/hello_world/main.c Sun Oct 26 16:37:46 2014
@@ -1,6 +1,26 @@
 #include <stdio.h>
+#if defined(__linux__)
+#include <sys/prctl.h>
 int main(int argc, char const *argv[]) {
+#if defined(__linux__)
+    // Immediately enable any ptracer so that we can allow the stub attach
+    // operation to succeed.  Some Linux kernels are locked down so that
+    // only an ancestor process can be a ptracer of a process.  This disables that
+    // restriction.  Without it, attach-related stub tests will fail.
+#if defined(PR_SET_PTRACER) && defined(PR_SET_PTRACER_ANY)
+    int prctl_result;
+    // For now we execute on best effort basis.  If this fails for
+    // some reason, so be it.
+    prctl_result = prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0);
+    (void) prctl_result;
     printf("Hello world.\n"); // Set break point at this line.
     if (argc == 1)
         return 0;

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