Fault Injection in strace [GSOC 2016]. A sample implementation.

[haris iqbal]

On Tue, Mar 8, 2016 at 10:00 PM, Gabriel Laskar <gabriel at lse.epita.fr> wrote:
> On Tue, 8 Mar 2016 18:30:37 +0530
> haris iqbal <haris.phnx at gmail.com> wrote:
>
>> Hello,
>>
>> I have implemented a very rudimentary option in strace to inject
>> faults for certain system calls. It uses the code written for the -e
>> option. One has to provide the system calls to be failed using the
>> newly implemented -g option. It seems to be working.
>>
>> Since it is not a patch, how should I share the code for everyone to
>> see.
>>
>
> Can't you give us a diff?

Yes. Here it is. I did this today evening, so the code might seem like
very temporary. I just wanted to check whether the way I am thinking
would work or not.

diff --git a/strace.c b/strace.c
index 49d6f3d..42cd9a6 100644
--- a/strace.c
+++ b/strace.c
@@ -1487,6 +1487,11 @@ get_os_release(void)
  * Don't want main() to inline us and defeat the reason
  * we have a separate function.
  */
+
+void fail_syscall(int);
+void set_fail_flag(void);
+void set_failing_parameters(char* str);
+
 static void ATTRIBUTE_NOINLINE
 init(int argc, char *argv[])
 {
@@ -1523,7 +1528,7 @@ init(int argc, char *argv[])
         "k"
 #endif
         "D"
-        "a:e:o:O:p:s:S:u:E:P:I:")) != EOF) {
+        "a:e:g:j:o:O:p:s:S:u:E:P:I:")) != EOF) {
         switch (c) {
         case 'b':
             if (strcmp(optarg, "execve") != 0)
@@ -1600,6 +1605,13 @@ init(int argc, char *argv[])
         case 'e':
             qualify(optarg);
             break;
+        case 'g':
+            qualify(optarg);
+            set_fail_flag();
+            break;
+        case 'j':
+            set_failing_parameters(optarg);
+            break;
         case 'o':
             outfname = xstrdup(optarg);
             break;
@@ -2322,7 +2334,8 @@ show_stopsig:
      * This should be syscall entry or exit.
      * Handle it.
      */
-    if (trace_syscall(tcp) < 0) {
+    int temp = trace_syscall(tcp);
+    if (temp < 0) {
         /*
          * ptrace() failed in trace_syscall().
          * Likely a result of process disappearing mid-flight.
@@ -2337,6 +2350,11 @@ show_stopsig:
         return true;
     }

+    if(temp == 3)
+    {
+        fail_syscall(pid);
+    }
+
 restart_tracee_with_sig_0:
     sig = 0;

diff --git a/syscall.c b/syscall.c
index 6efcde5..44fe5f3 100644
--- a/syscall.c
+++ b/syscall.c
@@ -785,12 +785,43 @@ static void get_error(struct tcb *, const bool);
 static int getregs_old(pid_t);
 #endif

+/* custom for POC of fault injection*/
+
+void fail_syscall(int);
+void set_fail_flag(void);
+void set_failing_parameters(const char*);
+
+
+
+unsigned int fail_flag = 0;
+int probability = 100;
+void set_fail_flag()
+{
+    fail_flag = 1;
+    return;
+}
+
+void set_failing_parameters(const char* str)
+{
+    probability = atoi(str);
+    return;
+}
+
+/* END */
+
+
 static int
 trace_syscall_entering(struct tcb *tcp)
 {
     int res, scno_good;

     scno_good = res = get_scno(tcp);
+    if ((tcp->qual_flg & QUAL_TRACE) && fail_flag == 1)
+    {
+        // probablity needs to be added using randon number genaratiion
+        tprintf("%s system called failed with probability %d\n",
syscall_name(tcp->scno), probability);
+        return 3;
+    }
     if (res == 0)
         return res;
     if (res == 1)
@@ -1241,6 +1272,16 @@ get_regset(pid_t pid)
 }
 #endif /* ARCH_REGS_FOR_GETREGSET */

+void fail_syscall(pid)
+{
+    void * fail_struct = calloc(1, sizeof(ARCH_IOVEC_FOR_GETREGSET));
+    tprintf("done");
+
+    ptrace(PTRACE_SETREGS, pid, NT_PRSTATUS, fail_struct);
+    free(fail_struct);
+}
+
+
 void
 get_regs(pid_t pid)
 {


>
> --
> Gabriel Laskar



-- 

With regards,

Md Haris Iqbal,
Placement Coordinator, MTech IT
NITK Surathkal,
Contact: +91 8861996962