Re: [PATCH 1/6] path.c: allocate enough memory for string

[Junio C Hamano <gitster@pobox.com>]

Stefan Beller <sbeller@google.com> writes:

> On Tue, Mar 29, 2016 at 5:57 PM, Eric Sunshine <sunshine@sunshineco.com> wrote:
>> On Tue, Mar 29, 2016 at 8:38 PM, Stefan Beller <sbeller@google.com> wrote:
>>> `strlen` returns the length of a string without the terminating null byte.
>>> To make sure enough memory is allocated we need to pass `strlen(..) + 1`
>>> to the allocation function.
>>>
>>> Signed-off-by: Stefan Beller <sbeller@google.com>
>>> ---
>>> diff --git a/path.c b/path.c
>>> @@ -155,7 +155,7 @@ static struct trie *make_trie_node(const char *key, void *value)
>>>         struct trie *new_node = xcalloc(1, sizeof(*new_node));
>>>         new_node->len = strlen(key);
>>>         if (new_node->len) {
>>> -               new_node->contents = xmalloc(new_node->len);
>>> +               new_node->contents = xmalloc(new_node->len + 1);
>>>                 memcpy(new_node->contents, key, new_node->len);
>>
>> Huh? This is a trie. It never accesses 'contents' as a NUL-terminated
>> string. Plus, no NUL is ever even copied, thus this is just
>> overallocating. How is this an improvement?
>
> By using strlen, I assumed it was a standard C string.
> I missed that, though.

You took hint from a wrong place.  You are auditing the destination
buffer, so the correct place to take hint from is the memcpy() that
touches the destination.