Introduce safety_limit and safe_range to protect against corrupt integer values; handle corrupt ob_type pointers

1 files changed, 20 insertions, 6 deletions

diff --git a/libpython.py b/libpython.py
index afb9869..8af75f5 100644
--- a/libpython.py
+++ b/libpython.py
@@ -52,6 +52,17 @@ import gdb
 class NullPyObjectPtr(RuntimeError):
     pass
 
+def safety_limit(val):
+    # Given a integer value from the process being debugged, limit it to some
+    # safety threshold so that arbitrary breakage within said process doesn't
+    # break the gdb process too much (e.g. sizes of iterations, sizes of lists)
+    return min(val, 100)
+
+def safe_range(val):
+    # As per range, but don't trust the value too much: cap it to a safety
+    # threshold in case the data was corrupted
+    return xrange(safety_limit(val))
+
 def is_py3k():
     # This code assumes that a libpython's DWARF data has actually been
     # loaded by the point that this function is called
@@ -150,6 +161,9 @@ class PyObjectPtr(object):
         except NullPyObjectPtr:
             # NULL tp_name?
             tp_name = 'unknown'
+        except RuntimeError:
+            # Can't even read the object at all?
+            tp_name = 'unknown'
         return FakeRepr(tp_name,
                         long(self._gdbval))
 
@@ -238,7 +252,7 @@ class PyDictObjectPtr(PyObjectPtr):
 
     def proxyval(self):
         result = {}
-        for i in xrange(self.field('ma_mask')):
+        for i in safe_range(self.field('ma_mask')):
             ep = self.field('ma_table') + i
             pvalue = PyObjectPtr.from_pyobject_ptr(ep['me_value'])
             if not pvalue.is_null():
@@ -285,7 +299,7 @@ class PyListObjectPtr(PyObjectPtr):
 
     def proxyval(self):
         result = [PyObjectPtr.from_pyobject_ptr(self[i]).proxyval()
-                  for i in range(int_from_int(self.field('ob_size')))]
+                  for i in safe_range(int_from_int(self.field('ob_size')))]
         return result
 
 class PyLongObjectPtr(PyObjectPtr):
@@ -321,7 +335,7 @@ class PyLongObjectPtr(PyObjectPtr):
             # FIXME: I haven't yet tested this case
             SHIFT = 30L
 
-        digits = [long(ob_digit[i]) * 2**(SHIFT*i) for i in xrange(abs(ob_size))]
+        digits = [long(ob_digit[i]) * 2**(SHIFT*i) for i in safe_range(abs(ob_size))]
         result = sum(digits)
         if ob_size < 0:
             result = -result
@@ -357,7 +371,7 @@ class PyTupleObjectPtr(PyObjectPtr):
 
     def proxyval(self):
         result = tuple([PyObjectPtr.from_pyobject_ptr(self[i]).proxyval()
-                        for i in range(int_from_int(self.field('ob_size')))])
+                        for i in safe_range(int_from_int(self.field('ob_size')))])
         return result
 
 class PyTypeObjectPtr(PyObjectPtr):
@@ -375,7 +389,7 @@ class PyUnicodeObjectPtr(PyObjectPtr):
 
         # Gather a list of ints from the Py_UNICODE array; these are either
         # UCS-2 or UCS-4 code points:
-        Py_UNICODEs = [int(field_str[i]) for i in xrange(field_length)]
+        Py_UNICODEs = [int(field_str[i]) for i in safe_range(field_length)]
 
         # Convert the int code points to unicode characters, and generate a
         # local unicode instance:
@@ -409,7 +423,7 @@ class FrameInfo:
         self.co_varnames = PyTupleObjectPtr.from_pyobject_ptr(self.co.field('co_varnames'))
         self.locals = [] # list of kv pairs
         f_localsplus = self.fval.field('f_localsplus')
-        for i in xrange(min(self.co_nlocals, 200)): # arbitrary upper sanity limit in case co_nlocals is corrupt
+        for i in safe_range(self.co_nlocals):
             #print 'i=%i' % i
             value = PyObjectPtr.from_pyobject_ptr(f_localsplus[i])
             if not value.is_null():