Check for ptrace_scope before doing ulp operations

YAMA has a security feature that block ptrace of non-child processes.
Check for that when the command is issued to make sure everything will
work as it should.

Signed-off-by: Giuliano Belinassi <[email protected]>

tools/ptrace.c

@@ -38,6 +38,7 @@
 #include <sys/wait.h>
 #include <time.h>
 #include <unistd.h>
+#include <assert.h>
 
 #include "error_common.h"
 #include "introspection.h"
@@ -401,15 +402,15 @@ attach(int pid)
 
   if (ulp_ptrace(PTRACE_ATTACH, pid, NULL, NULL)) {
     DEBUG("PTRACE_ATTACH error: %s.\n", strerror(errno));
-    return 1;
+    return errno;
   }
 
   while (true) {
     pid_t ret = waitpid(pid, &status, WSTOPPED);
 
     if (ret == -1) {
       DEBUG("waitpid error (pid %d): %s.\n", pid, strerror(errno));
-      return 1;
+      return errno;
     }
     else if (ret == pid) {
 
@@ -608,3 +609,33 @@ run_and_redirect(int pid, struct user_regs_struct *regs, ElfW(Addr) routine)
 
   return 0;
 }
+
+
+/** @brief Check ptrace scope security option.
+ *
+ * In some systems, ptracing a simbling process is disalowed with a permission
+ * error.  This function will check if we are in such case, which we should
+ * error out and instruct the user what to do.
+ *
+ * @return:      true if ptrace of simblings works.
+ **/
+bool
+check_ptrace_scope(void)
+{
+  if (geteuid() == 0) {
+    /* Running as root.  No problem.  */
+    return true;
+  }
+
+  FILE *f = fopen("/proc/sys/kernel/yama/ptrace_scope", "r");
+  if (f == NULL) {
+    /* YAMA is not running.  */
+    return true;
+  }
+
+  unsigned char buf[4] = {0};
+  size_t n = fread(buf, sizeof(unsigned char), 4, f);
+  assert(n == 2 && "What is in the ptrace_scope?");
+  fclose(f);
+  return buf[0] == '0' ? true : false;
+}

tools/ptrace.h

@@ -26,9 +26,13 @@
 #include <sys/ptrace.h>
 #include <sys/user.h>
 #include <sys/wait.h>
+#include <stdbool.h>
 
 #include "ulp_common.h"
 
+/* System configuration options.  */
+bool check_ptrace_scope(void);
+
 /* Memory read/write helper functions */
 
 int write_bytes_ptrace(const void *buf, size_t n, int pid, Elf64_Addr addr);

tools/ulp.c

@@ -450,6 +450,28 @@ change_color(const char *ansi_escape)
   }
 }
 
+static bool
+requires_ptrace(command_t command)
+{
+  switch(command) {
+    case ULP_NONE:
+    case ULP_DUMP:
+    case ULP_POST:
+    case ULP_EXTRACT:
+    case ULP_PACKER:
+    case ULP_LIVEPATCHABLE:
+      return false;
+
+    case ULP_PATCHES:
+    case ULP_TRIGGER:
+    case ULP_CHECK:
+    case ULP_MESSAGES:
+    case ULP_SET_PATCHABLE:
+      return true;
+  }
+  return false;
+}
+
 int
 main(int argc, char **argv, char *envp[] __attribute__((unused)))
 {
@@ -476,6 +498,17 @@ main(int argc, char **argv, char *envp[] __attribute__((unused)))
 
   argp_parse(&argp, argc, argv, 0, 0, &arguments);
 
+
+  /* Check if command requires ptrace.  */
+  if (requires_ptrace(arguments.command) &&
+        check_ptrace_scope() == false) {
+    WARN("System has 'ptrace_scope' enabled. Please become root or disable it"
+         "by setting:\n\n"
+         "$ sudo echo 0 > /proc/sys/kernel/yama/ptrace_scope\n\n"
+         "and try again.");
+    return EPERM;
+  }
+
   switch (arguments.command) {
     case ULP_NONE:
       ret = 1;