tools: ynl-gen: improve unwind on parsing errors

When parsing multi-attr we count the objects and then allocate
an array to hold the parsed objects. If an attr space has multiple
multi-attr objects, however, if parsing the first array fails
we'll leave the object count for the second even tho the second
array was never allocated.

This may cause crashes when freeing objects on error.

Count attributes to a variable on the stack and only set the count
in the object once the memory was allocated.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/ynl-gen-c.py

@@ -488,7 +488,7 @@ class TypeMultiAttr(Type):
             raise Exception(f"Sub-type {self.attr['type']} not supported yet")
 
     def _attr_get(self, ri, var):
-        return f'{var}->n_{self.c_name}++;', None, None
+        return f'n_{self.c_name}++;', None, None
 
     def attr_put(self, ri, var):
         if self.attr['type'] in scalars:
@@ -1306,6 +1306,11 @@ def _multi_parse(ri, struct, init_lines, local_vars):
         local_vars.append('struct ynl_parse_arg parg;')
         init_lines.append('parg.ys = yarg->ys;')
 
+    all_multi = array_nests | multi_attrs
+
+    for anest in sorted(all_multi):
+        local_vars.append(f"unsigned int n_{struct[anest].c_name} = 0;")
+
     ri.cw.block_start()
     ri.cw.write_func_lvar(local_vars)
 
@@ -1316,6 +1321,11 @@ def _multi_parse(ri, struct, init_lines, local_vars):
     for arg in struct.inherited:
         ri.cw.p(f'dst->{arg} = {arg};')
 
+    for anest in sorted(all_multi):
+        aspec = struct[anest]
+        ri.cw.p(f"if (dst->{aspec.c_name})")
+        ri.cw.p(f'return ynl_error_parse(yarg, "attribute already present ({struct.attr_set.name}.{aspec.name})");')
+
     ri.cw.nl()
     ri.cw.block_start(line=iter_line)
 
@@ -1331,8 +1341,9 @@ def _multi_parse(ri, struct, init_lines, local_vars):
     for anest in sorted(array_nests):
         aspec = struct[anest]
 
-        ri.cw.block_start(line=f"if (dst->n_{aspec.c_name})")
-        ri.cw.p(f"dst->{aspec.c_name} = calloc(dst->n_{aspec.c_name}, sizeof(*dst->{aspec.c_name}));")
+        ri.cw.block_start(line=f"if (n_{aspec.c_name})")
+        ri.cw.p(f"dst->{aspec.c_name} = calloc({aspec.c_name}, sizeof(*dst->{aspec.c_name}));")
+        ri.cw.p(f"dst->n_{aspec.c_name} = n_{aspec.c_name};")
         ri.cw.p('i = 0;')
         ri.cw.p(f"parg.rsp_policy = &{aspec.nested_render_name}_nest;")
         ri.cw.block_start(line=f"mnl_attr_for_each_nested(attr, attr_{aspec.c_name})")
@@ -1346,8 +1357,9 @@ def _multi_parse(ri, struct, init_lines, local_vars):
 
     for anest in sorted(multi_attrs):
         aspec = struct[anest]
-        ri.cw.block_start(line=f"if (dst->n_{aspec.c_name})")
-        ri.cw.p(f"dst->{aspec.c_name} = calloc(dst->n_{aspec.c_name}, sizeof(*dst->{aspec.c_name}));")
+        ri.cw.block_start(line=f"if (n_{aspec.c_name})")
+        ri.cw.p(f"dst->{aspec.c_name} = calloc(n_{aspec.c_name}, sizeof(*dst->{aspec.c_name}));")
+        ri.cw.p(f"dst->n_{aspec.c_name} = n_{aspec.c_name};")
         ri.cw.p('i = 0;')
         if 'nested-attributes' in aspec:
             ri.cw.p(f"parg.rsp_policy = &{aspec.nested_render_name}_nest;")