[memory] Fix read_cstring trying to read too far (#1112)

gef.py

@@ -10742,8 +10742,24 @@ def read_cstring(self,
         try:
             res_bytes = self.read(address, length)
         except gdb.error:
-            err(f"Can't read memory at '{address}'")
-            return ""
+            current_address = address
+            res_bytes = b""
+            while len(res_bytes) < length:
+                try:
+                    # Calculate how many bytes there are until next page
+                    next_page = current_address + DEFAULT_PAGE_SIZE
+                    page_mask = ~(DEFAULT_PAGE_SIZE - 1)
+                    size = (next_page & page_mask) - current_address
+
+                    # Read until the end of the current page
+                    res_bytes += self.read(current_address, size)
+
+                    current_address += size
+                except gdb.error:
+                    if not res_bytes:
+                        err(f"Can't read memory at '{address:#x}'")
+                        return ""
+                    break
         try:
             with warnings.catch_warnings():
                 # ignore DeprecationWarnings (see #735)

tests/api/gef_memory.py

@@ -178,3 +178,17 @@ def test_func_parse_maps_realpath(self):
                    "/usr" not in section.realpath):
                     assert pathlib.Path(section.realpath).is_file()
                     break
+
+    def test_func_read_cstring_oob(self):
+        gef, gdb = self._gef, self._gdb
+
+        gdb.execute("b main")
+        gdb.execute("start")
+
+        section = gef.memory.maps[0]
+        oob_val = gef.memory.read_cstring(section.page_start, section.page_end -
+                                section.page_start + 0x100)
+        val = gef.memory.read_cstring(section.page_start, section.page_end -
+                                section.page_start)
+
+        assert val == oob_val