[FFmpeg-devel] [PATCH]lavu/mem: Make alloc array functions more similar to av_malloc

[James Almer]

On 4/12/2020 5:55 PM, Carl Eugen Hoyos wrote:
> Am So., 12. Apr. 2020 um 22:48 Uhr schrieb James Almer <jamrial at gmail.com>:
>>
>> On 4/11/2020 8:53 PM, Carl Eugen Hoyos wrote:
>>> Am So., 12. Apr. 2020 um 00:44 Uhr schrieb Carl Eugen Hoyos
>>> <ceffmpeg at gmail.com>:
>>>>
>>>> Am So., 5. Apr. 2020 um 14:03 Uhr schrieb Michael Niedermayer
>>>> <michael at niedermayer.cc>:
>>>>>
>>>>> On Sat, Apr 04, 2020 at 12:46:36AM +0200, Carl Eugen Hoyos wrote:
>>>>>> Hi!
>>>>>>
>>>>>> Attached patch makes the alloc array functions more similar to
>>>>>> av_malloc, depending on max_alloc_size instead of INT_MAX.
>>>>>>
>>>>>> Allows a work-around for ticket #7140
>>>>>>
>>>>>> Please comment, Carl Eugen
>>>>>
>>>>>>  mem.c |    8 ++++----
>>>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>>>> 507531ed6f0932834d005bc1dd7d18e762f158b2  0001-lavu-mem-Make-alloc-array-functions-more-similar-to-.patch
>>>>>> From 7ae240a9f7885130251031aba5d0764b11947fec Mon Sep 17 00:00:00 2001
>>>>>> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
>>>>>> Date: Sat, 4 Apr 2020 00:37:03 +0200
>>>>>> Subject: [PATCH] lavu/mem: Make alloc array functions more similar to
>>>>>>  av_malloc().
>>>>>>
>>>>>> Do not limit the array allocation functions to allocations of INT_MAX,
>>>>>> instead depend on max_alloc_size like av_malloc().
>>>>>>
>>>>>> Allows a workaround for ticket #7140.
>>>>>> ---
>>>>>>  libavutil/mem.c | 8 ++++----
>>>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>>>
>>>>> av_size_mult() may be faster
>>>>
>>>> New patch attached.
>>>
>>> And an actually working variant.
>>>
>>> Please comment, Carl Eugen
>>
>>> From 643c501d6698d7d17e47a9f907165649f1446fa6 Mon Sep 17 00:00:00 2001
>>> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
>>> Date: Sun, 12 Apr 2020 00:36:30 +0200
>>> Subject: [PATCH] lavu/mem: Make other alloc functions more similar to av_malloc().
>>>
>>> Do not limit the array allocation functions and av_calloc() to allocations
>>> of INT_MAX, instead depend on max_alloc_size like av_malloc().
>>>
>>> Allows a workaround for ticket #7140.
>>> ---
>>>  libavutil/mem.c | 20 ++++++++++++--------
>>>  1 file changed, 12 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/libavutil/mem.c b/libavutil/mem.c
>>> index 88fe09b179..e044374c62 100644
>>> --- a/libavutil/mem.c
>>> +++ b/libavutil/mem.c
>>> @@ -183,23 +183,26 @@ int av_reallocp(void *ptr, size_t size)
>>>
>>>  void *av_malloc_array(size_t nmemb, size_t size)
>>>  {
>>> -    if (!size || nmemb >= INT_MAX / size)
>>> +    size_t result;
>>> +    if (av_size_mult(nmemb, size, &result) < 0)
>>>          return NULL;
>>> -    return av_malloc(nmemb * size);
>>> +    return av_malloc(result);
>>
>> If I'm reading this right, when size is 0, instead of NULL this will now
>> return av_malloc(0), which looks like it may end up being a pointer to a
>> 1 byte big buffer. Is that intended?
>>
>> The previous version you sent apparently considered that scenario.
> 
> But it did not pass fate because the behaviour before the patch
> was not to return NULL for alloc(0).

Before this patch it would return NULL when size was 0 and alloc(0) when
nmemb was 0. Now it will return alloc(0) when either of the two
arguments is 0.

The check should be (!size || av_size_mult(nmemb, size, &result) < 0) or
similar instead, if we want to keep the original behavior.