Re: [PATCH 1/6] path.c: allocate enough memory for string
Stefan Beller writes:
> On Tue, Mar 29, 2016 at 5:57 PM, Eric Sunshine
> wrote:
>> On Tue, Mar 29, 2016 at 8:38 PM, Stefan Beller 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
>>> ---
>>> 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.
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Re: [PATCH 1/6] path.c: allocate enough memory for string
On Tue, Mar 29, 2016 at 5:57 PM, Eric Sunshine wrote:
> On Tue, Mar 29, 2016 at 8:38 PM, Stefan Beller 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
>> ---
>> 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.
>
>> }
>> new_node->value = value;
>> --
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Re: [PATCH 1/6] path.c: allocate enough memory for string
Stefan Beller writes:
> `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
> ---
> path.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/path.c b/path.c
> index 969b494..0ae8af5 100644
> --- 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);
> }
This structure looks like a counted string that does not
want to have a terminating NUL after the contents, judging from the
way memcpy() copies only len and not len+1.
Did I write this (wondering why this was addressed to me)?
> new_node->value = value;
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Re: [PATCH 1/6] path.c: allocate enough memory for string
On Tue, Mar 29, 2016 at 8:38 PM, Stefan Beller 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
> ---
> 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?
> }
> new_node->value = value;
> --
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