Fixes: signed integer overflow: -2147483634 - 16 cannot be represented in type 'int'
Fixes: 28322/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-5711888402612224
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 74c4c53953)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
Fixes: signed integer overflow: -2147483648 - 4 cannot be represented in type 'int'
Fixes: 28127/clusterfuzz-testcase-minimized-ffmpeg_dem_VOC_fuzzer-4880586455646208
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 52f75181bf)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
Fixes: signed integer overflow: 7 - -2147483647 cannot be represented in type 'int'
Fixes: 28036/clusterfuzz-testcase-minimized-ffmpeg_dem_MICRODVD_fuzzer-5171698751766528
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit f569ac4ce0)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This fixes leaks when the trailer is never written.
Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 848f96a2a6)
seg_init() and seg_write_header() currently contain a few error paths
in which an already opened AVIOContext for the child muxer leaks (namely
if there are unrecognized options for the child muxer or if writing the
header of the child muxer fails); the reason for this is that this
AVIOContext is not closed in the deinit function. If all goes well, it
is closed when writing the trailer. From this it also follows that the
AVIOContext also leaks when the trailer is never written, even when
writing the header succeeds.
But simply freeing said AVIOContext in the deinit function is
complicated by the fact that the AVIOContext may or may not have been
opened via the io_open callback: If options are set to discard header
and trailer, said AVIOContext can also be a null context which must not
be closed via the io_close callback. This may lead to crashes, as
io_close may presume the AVIOContext's opaque to be set. It currently
works with the default io_close callback which simply calls avio_close(),
because avio_close() doesn't care about opaque being NULL since commit
6e8e8431e1. Therefore this commit records
which of the two kinds of AVIOContext is currently in use to use the
right way to close it.
Finally there was one instance (namely if initializing the child muxer
fails with no unrecognized options) where the AVIOContext was always
closed via the io_close callback. The above remark applies to this; it
has been fixed, too.
Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 30de02998d)
A string containing the segment's filename that the segment muxer
allocates got only freed in its write_trailer function. This implies
that it leaks if write_trailer is never called, e.g. if initializing
the child muxer fails. This commit fixes this by freeing the string
in the deinit function instead.
Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 3152a2a218)
The segment muxer has an option to output a file containing a list of
the segments written. The AVIOContext used for writing this file is
opened via the main AVFormatContext's io_open callback; seg_free()
meanwhile unconditionally closes this AVIOContext by calling
ff_format_io_close() with the child muxer (the one for the actual output
format) as AVFormatContext.
The problem hereby is that the child AVFormatContext need not exist,
even when the AVIOContext does. This leads to a segfault in
ff_format_io_close() when the child muxer's io_close callback is called.
Situations in which the AVFormatContext can be NULL range from an
invalid reference stream parameter to an unavailable/bogus/unsupported
output format to inability to allocate the AVFormatContext.
The solution is to simply close the AVIOContext with the AVFormatContext
that was used to open it: The main AVFormatContext.
Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 936d967871)
If the user has set none of the options specifying the segments'
durations, a default value of 2s is used by duplicating a "2" string and
using av_parse_time() on it. Yet duplicating the string was unchecked
and if the allocation failed, one would get a segfault in
av_parse_time().
This commit solves this by turning said option into an option of type
AV_OPT_TYPE_DURATION (which also uses av_parse_time() internally),
avoiding duplicating the string altogether.
Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 06f99cc4dd)
The code to free them is not in the segment muxer's deinit function,
but in its write_trailer function which means that these lists leak if
write_trailer isn't called after their allocation. This happens e.g. if
the given lists are invalid (e.g. consisting only of ',' (which delimit
entries)), so that parsing them fails and so does the muxer's init
function; write_trailer is then never called.
This has been fixed by moving the code to free them to the deinit
function.
Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 4b836c8613)
The segment muxer copies the user-provided AVCodecParameters to the
newly created child streams in its init function before initializing the
child muxer; and since commit 8e6478b723,
it does this again before calling avformat_write_header() if that is
called from seg_write_header(). The reason for this is complicated:
At that time writing the header was delayed, i.e. it was not triggered
by avformat_write_header() (unless the AVFMT_FLAG_AUTO_BSF was unset),
but instead by writing the very first packet. The rationale behind this
was to allow to run bitstream filters on the packets in the interleavement
queue in order to generate missing extradata from them before the muxer's
write_header function is actually called.
The segment muxer went even further: It initialized the child muxer and
ran the child muxer's check_bitstream functions on the packets in its
own muxing queue and stole any bitstream filters that got inserted. The
reason for this is that the segment muxer has an option to write the
header to a separate file and for this it is needed to write the child
muxer's header without delay, but with correct extradata. Unsetting
AVFMT_FLAG_AUTO_BSF for the child muxer accomplished the first goal and
stealing the bitstream filters the second; and in order for the child
muxer to actually use the updated extradata, the old AVCodecParameters
(set before avformat_init_output()) were overwritten with the new ones.
Updating the extradata proceeded as follows: The bitstream filter itself
simply updated the AVBSFContext's par_out when processing a packet, in
violation of the new BSF API (where par_out may only be set in the init
function); the muxing code then simply forwarded the updated extradata,
overwriting the par_in of the next BSF in the BSF chain with the fresh
par_out of the last one and the AVStream's par with the par_out of the
last BSF. This was an API violation, too, of course, but it made
remuxing ADTS AAC into mp4/matroska work.
But this no longer serves a useful purpose since the aac_adtstoasc BSF
was updated to propagate new extradata via packet side data in commit
f63c351657; the next commit then removed
the code in mux.c passing new extradata along the filter chain. This
alone justifies removing the code for setting the AVCodecParameters a
second time.
But there is even another reason to do so: It is harmful. The ogg muxer
parses the extradata of Theora and Vorbis in its init function and keeps
pointers to parts of it. Said pointers become dangling when the
extradata is overwritten by the segment muxer, leading to
use-after-frees as has happened in ticket #8881 which this commit fixes.
Ticket #8517 is about another issue caused by this: Immediately after
having overwritten the old AVCodecParameters the segment muxer checks
whether the codec_tag is ok (the codec_tag is set generically when
initializing the child muxer based upon muxer-specific lists). The check
used is: If the child output format has such a list and if the codec tag
of the non-child stream does not match the codec id given the list of
codec tags and if there is a match for the codec id in the codec tag
list, then set the codec tag to zero (and not to the existing match),
otherwise set the codec tag of the child stream to the codec tag
of the corresponding stream of the main AVFormatContext (which is btw
redundant given that the child AVCodecParameters have just been
overwritten with the AVCodecParameters of the corresponding stream of
the main AVFormatContext).
Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 92c8b79b5a)
This is currently safe here, because the effective lifetime of
adaptionset_lang is parse_manifest_adaptationset() (i.e. the pointer
gets overwritten each time on entry to the function and gets freed
before exiting the function), but it is nevertheless safer to reset the
pointer.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 616eb93a40)
Use xmlFree instead of av_freep
snip from libxml2:
* xmlGetProp:
...
* Returns the attribute value or NULL if not found.
* It's up to the caller to free the memory with xmlFree().
According to libxml2, you are supposed to use xmlFree instead of free
on the pointer returned by it, and also using av_freep on Windows will
call _aligned_free instead of normal free, causing _aligned_free to raise
SIGTRAP and crashing ffmpeg and ffplay.
Signed-off-by: Christopher Degawa <ccom@randomderp.com>
(cherry picked from commit 0117d5aa03)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
get_content_url() allocates two buffers for temporary strings and when
one of them couldn't be allocated, it simply returns, although one of
the two allocations could have succeeded and would leak in this
scenario. This can be fixed by avoiding one of the temporary buffers.
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 0f9ade1ff3)
Up until now, the DASH demuxer used av_dynarray_add() to add
audio/video/subtitles representations to arrays. Yet av_dynarray_add()
frees the array upon failure, leading to leaks of its elements;
furthermore, the element to be added leaks, too.
This has been fixed by using av_dynarray_add_nofree() instead and by
freeing the elements that could not be added to the list. Furthermore,
errors from this are now checked and returned.
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit d63f8c873b)
These languages are normally freed after having been added as metadata
to their respective AVStreams. Yet if one never reaches said point, they
leak. This can happen as a result of an error when reading the header or
as a result of refreshing the manifests.
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit f1c3c173c9)
The DASH demuxer currently extracts several strings at once from an xml
document before processing them one by one; these strings are allocated,
stored in local variables and need to be freed by the demuxer itself.
So if an error happens when processing one of them, all strings need to
be freed before returning. This has simply not been done, leading to
leaks.
A simple fix would be to add the necessary code for freeing; yet there is
a better solution: Avoid having several strings at the same time by
extracting a string, processing it and immediately freeing it. That way
one only has to free at most one string on error.
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit e7aea1fe73)
If parsing a representation fails, it is not added to the list of
representations and is therefore not freed in dash_close(); it therefore
leaked in most error paths in parse_manifest_representation() (some
error paths had (incomplete) code for freeing). This commit fixes
freeing the representation in this case.
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 5c91701dc7)
It is always zero. Also remove other unused elements.
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 5d63f154ef)
open_url() in the DASH as well in the hls demuxer share a common bug:
They modify an AVDictionary (i.e. set a new entry) given to them as
AVDictionary *, yet if this new entry leads to reallocation and
relocation of the AVDictionary, the caller's pointer will become
dangling, leading to use-after-frees. So pass an AVDictionary **.
(With the current implementation of AVDictionary the above can only
happen if the AVDictionary was empty initially (in which case the
new AVDictionary leaks); furthermore if the I/O is ordinary (i.e. opened
by avio_open2() or ffio_open_whitelist()), the dict is never empty (it
contains an rw_timeout entry from save_avio_options()). So this issue
could only happen if the caller sets a nondefault io_open callback, but
no AVIOContext (the AVFMT_FLAG_CUSTOM_IO flag won't be set in this
case). In case of the HLS demuxer, it was also necessary that setting
the "seekable" entry failed. Yet one should simply not rely on internals
of the AVDict API.)
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit ac2852d795)
Just postpone the allocation of the dict until it is really needed
(after the checks that can fail).
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 4b8fdf70a8)
This currently doesn't cause any trouble, because the only caller did
not clean up the representation upon error at all; but fixing this is
a prerequisite for doing so.
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 01a4c35969)
The code in question seems to have been copied from about 70 lines
above; yet the code here is only executed if some of the variables
(namely representation_segmenttemplate_node and fragment_template_node)
are NULL, so it makes no sense to check them for a child element.
Also remove a redundant resetting of a pointer to an AVFormatContext
after avformat_close_input() (which already sets the pointer to NULL).
Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 248ef276be)
Up until now, the wav muxer used a reallocation of the form ptr =
av_realloc(ptr, size); that leaks upon error. Furthermore, if a
failed reallocation happened when writing the trailer, a segfault
would occur due to avio_write(NULL, size) because the muxer only
prints an error message upon allocation error, but does not return
the error.
Moreover setting the pointer to the buffer to NULL on error seems to
be done on purpose in order to record that an error has occured so that
outputting the peak values is no longer attempted. This behaviour has
been retained by simply disabling whether peak data should be written
if an error occurs.
Finally, the reallocation is now done once per peak block and not once
per peak block per channel; it is also done with av_fast_realloc and not
with a linear size increase.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 19ae873252)
Do this by moving the check before the allocation.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 4294f64d57)
The MPEG-PS muxer uses a custom queue of custom packets. To keep track
of it, it has a pointer (named predecode_packet) to the head of the
queue and a pointer to where the next packet is to be added (it points
to the next-pointer of the last element of the queue); furthermore,
there is also a pointer that points into the queue (called premux_packet).
The exact behaviour was as follows: If premux_packet was NULL when a
packet is received, it is taken to mean that the old queue is empty and
a new queue is started. premux_packet will point to the head of said
queue and the next_packet-pointer points to its next pointer. If
predecode_packet is NULL, it will also made to point to the newly
allocated element.
But if premux_packet is NULL and predecode_packet is not, then there
will be two queues with head elements premux_packet and
predecode_packet. Yet only elements reachable from predecode_packet are
ever freed, so the premux_packet queue leaks.
Worse yet, when the predecode_packet queue will be eventually exhausted,
predecode_packet will be made to point into the other queue and when
predecode_packet will be freed, the next pointer of the preceding
element of the queue will still point to the element just freed. This
element might very well be still reachable from premux_packet which
leads to use-after-frees lateron. This happened in the tickets mentioned
below.
Fix this by never creating two queues in the first place by checking for
predecode_packet to know whether the queue is empty. If premux_packet is
NULL, then it is set to the newly allocated element of the queue.
Fixes tickets #6887, #8188 and #8266.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit cfce16449c)
mxf distinguishes codec profiles by different UIDs and therefore needs
to check that the input is actually compatible with mxf (i.e. if there
is a defined UID for it). If not, then sometimes the UID would be set to
NULL and writing the (video) packet would fail. Yet the following audio
packet would trigger writing the header (which has been postponed because
the UID is not known at the start) and if the UID is NULL, this can lead
to segfaults. This commit therefore stops setting the UID to NULL if the
input is incompatible with mxf (it has initially been set to a generic
value in mxf_write_header()).
Fixes#7993.
Reviewed-by: Tomas Härdin <tjoppen@acc.umu.se>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 5400e4a50c)
Such a scenario is undefined behaviour and would also indicate a bug
in our code.
Suggested-by: James Almer <jamrial@gmail.com>
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit da857099e9)
This is undefined behaviour in C, so use data = len ? data + len : data
instead of data += len. GCC optimizes the branch away in this case;
Clang unfortunately doesn't.
Fixes ticket #8592.
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 9c0b3eddf4)
The FLAC muxer currently stores an attached picture corresponding to an
AVStream in AVStream.priv_data. The AVPacket contained therein is
unreferenced after it has been written. The AVPacket structure itself is
then freed generically as AVStream.priv_data.
And this can lead to memleaks if an attached picture is not written:
It might be because the trailer is never written or because writing
a previous attached picture failed in case error_recognition is set
to explode.
Therefore free the packets properly (i.e. with av_packet_free())
in the muxer's deinit function.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 029cf6a91c)
The ASF file format has a limit of 127 streams and the "asf_o" demuxer
(the ASF demuxer from Libav) has an array of pointers for a structure
called ASFStream that is allocated on demand for every stream. Attached
pictures are not streams in the sense of the ASF specification, yet the
demuxer created an ASFStream for them; and in one codepath it also
forgot to check whether the array of ASFStreams is already full. The
result is a write beyond the end of the array and a segfault lateron.
Fixing this is easy: Don't create ASFStreams for attached picture
streams.
(Other results of the current state of affairs are unnecessary allocations
(of ASFStreams structures), the misparsing of valid files (there might not
be enough ASFStreams left for the valid streams if attached pictures take
up too many); furthermore, the ASFStreams created for attached pictures all
have the stream number 0, an invalid stream number (the valid range is
1-127). This means that invalid data (packets for a stream with stream
number 0) won't get rejected lateron.)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit e83f27a21a)
apng data consists of parts containing a small header (including a
four-byte size field) and a data part; the size field does not account
for everything and is actually twelve bytes short of the actual size. In
order to make sure that the size fits into an int, the size field is
checked for being > INT_MAX; yet this does not account for the + 12 and
upon conversion to int (which happens when calling append_extradata()),
the size parameter can still wrap around. In this case the currently
used check would lead to undefined signed integer overflow.
Furthermore, append_extradata() appends the new data to the already
existing extradata and therefore needs to make sure that the combined
size of new and old data as well as padding fits into an int. The check
used for this is "if (old_size > INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE -
new_size)". If new_size is > INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE
the right side becomes negative if the types are signed (as they are
now); yet changing this to "if (new_size > INT_MAX -
AV_INPUT_BUFFER_PADDING_SIZE - old_size)" is better as this also works
for unsigned types (where it is of course presumed that INT_MAX is
replaced by the corresponding maximum for the new type).
Both of these issues have been fixed.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 9c341c6c92)
If avio_read() could read anything, it returns the number of bytes read,
even if it could not read as much as the caller desired.
apng_read_header() only checked the return value of its avio_read() calls
for being negative and this meant that it was possible for an incomplete
header to not be detected. The return value of the last successfull call
has been returned instead. This commit changes this.
Fixes: OOM
Fixes: 26608/clusterfuzz-testcase-minimized-ffmpeg_dem_APNG_fuzzer-4839491644424192
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 2cf1eefae5)
Regression since 715ff75e5d.
Fixes Coverity issues #1468654 and #1468656.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 11ea0ed20e)
The buffers used when fragmented output is enabled have up until now not
been freed in the deinit function; they leak e.g. if one errors out of
mov_write_trailer() before one reaches the point where they are normally
written out and freed. This can e.g. happen if allocating new vos_data
fails at the beginning of mov_write_trailer().
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit e3b5316bed)
Otherwise the old data leaks whenever extradata needs to be rewritten
(e.g. when encoding FLAC with our encoder that sends an updated
extradata packet at the end).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 432f291dff)
When remuxing an rtp hint stream (or any stream with the tag "rtp "),
the mov muxer treats this as one of the rtp hint tracks it creates
internally when ordered to do so; yet this track lacks the
AVFormatContext for the hinting rtp muxer, leading to segfaults in
mov_write_udta_sdp() if a "trak" atom is written for this stream; if not,
the stream's codecpar is freed by mov_free() as if the mov muxer owned
it (it does for the internally created "rtp " tracks), but without
resetting st->codecpar, leading to double-frees lateron. This commit
therefore ignores said tag which makes rtp hint streams unremuxable.
This fixes tickets #8181 and #8186.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 22c3cd1760)
There are two possible kinds of timecode tracks (with tag "tmcd") in the
mov muxer: Tracks created internally by the muxer and timecode tracks
sent by the user. If any of the latter exists, the former are
deactivated. The former all belong to another track, the source
track; the latter don't have a source track set, but the index of the
source track is initially zeroed by av_mallocz_array(). This is a
problem since 3d894db700: Said commit added
a function that calculates the duration of tracks and the duration of
timecode tracks is calculated by rescaling the duration (calculated by
the very same function) of the source track. This gives an infinite
recursion if the first track (the one that will be treated as source
track for all timecode tracks) is a timecode track itself, leading to a
stack overflow.
This commit fixes this by not using the nonexistent source track
when calculating the duration of timecode tracks not created internally
by the mov muxer.
Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 22a2386a56)
The earlier code would first attempt to allocate two buffers, then
attempt to allocate an AVIOContext, using one of the new buffers I/O
buffer, then check the allocations. On success, a z_stream that is used
in the AVIOContext's read_packet callback is initialized afterwards.
There are two problems with this: In case the allocation of the I/O
buffer fails avio_alloc_context() will be given a NULL read buffer
with a size > 0. This works right now, but it is fragile. The second
problem is that the z_stream used in the read_packet callback is not
functional when avio_alloc_context() is allocated (it might be that
avio_alloc_context() might already fill the buffer in the future). This
commit fixes both of these problems by reordering the operations.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 3f04c30372)
