[FFmpeg-devel] [PATCH] libavutil/encryption_info: Add NULL checks.

[Carl Eugen Hoyos]

2018-06-04 18:59 GMT+02:00, Jacob Trimble <modmaker-at-google.com at ffmpeg.org>:
> On Fri, Jun 1, 2018 at 5:03 PM Michael Niedermayer
> <michael at niedermayer.cc> wrote:
>>
>> On Thu, May 31, 2018 at 09:33:36AM -0700, Jacob Trimble wrote:
>> > Found by Chrome's ClusterFuzz: http://crbug.com/846662.
>> >
>> > Signed-off-by: Jacob Trimble <modmaker at google.com>
>> > ---
>> >  libavutil/encryption_info.c | 7 +++++--
>> >  1 file changed, 5 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/libavutil/encryption_info.c b/libavutil/encryption_info.c
>> > index 20a752d6b4..a48ded922c 100644
>> > --- a/libavutil/encryption_info.c
>> > +++ b/libavutil/encryption_info.c
>> > @@ -64,6 +64,8 @@ AVEncryptionInfo *av_encryption_info_clone(const
>> > AVEncryptionInfo *info)
>> >  {
>> >      AVEncryptionInfo *ret;
>> >
>> > +    if (!info)
>> > +        return NULL;
>> >      ret = av_encryption_info_alloc(info->subsample_count,
>> > info->key_id_size, info->iv_size);
>> >      if (!ret)
>> >          return NULL;
>>
>> > @@ -127,7 +129,7 @@ uint8_t *av_encryption_info_add_side_data(const
>> > AVEncryptionInfo *info, size_t *
>> >      uint8_t *buffer, *cur_buffer;
>> >      uint32_t i;
>> >
>> > -    if (UINT32_MAX - FF_ENCRYPTION_INFO_EXTRA < info->key_id_size ||
>> > +    if (!info || !size || UINT32_MAX - FF_ENCRYPTION_INFO_EXTRA <
>> > info->key_id_size ||
>> >          UINT32_MAX - FF_ENCRYPTION_INFO_EXTRA - info->key_id_size <
>> > info->iv_size ||
>> >          (UINT32_MAX - FF_ENCRYPTION_INFO_EXTRA - info->key_id_size -
>> > info->iv_size) / 8 < info->subsample_count) {
>> >          return NULL;
>> > @@ -260,7 +262,8 @@ uint8_t *av_encryption_init_info_add_side_data(const
>> > AVEncryptionInitInfo *info,
>> >      uint8_t *buffer, *cur_buffer;
>> >      uint32_t i, max_size;
>> >
>> > -    if (UINT32_MAX - FF_ENCRYPTION_INIT_INFO_EXTRA <
>> > info->system_id_size ||
>> > +    if (!info || !side_data_size ||
>> > +        UINT32_MAX - FF_ENCRYPTION_INIT_INFO_EXTRA <
>> > info->system_id_size ||
>> >          UINT32_MAX - FF_ENCRYPTION_INIT_INFO_EXTRA -
>> > info->system_id_size < info->data_size) {
>> >          return NULL;
>> >      }
>>
>> in which valid case would these be called with NULL input ?
>> iam asking as this feels as if it might be a bug in teh caller
>>
>
> This was found by Chrome's ClusterFuzz, which I am not that familiar
> with.  I think it was just running fuzz tests directly on FFmpeg code,
> so it wasn't in production code.  But since this is a public method,
> we should validate the input in any case.

How do you validate the size of C buffers in general?

Carl Eugen