Memory leak in v4l2 input device if setting timestamps option to mono2abs or abs

[bermond]

Summary of the bug:
ASan reports a memory leak when closing a 'v4l2' input device if the 'timestamps' option is setted to 'mono2abs' or 'abs'. These values convert the start timestamp.

Using the value 'default' (which does not convert start timestamp) does not cause a memory leak.

How to reproduce:

#include <stdio.h>
#include <libavdevice/avdevice.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libavutil/avutil.h>

int main() {
    int ret;
    AVDictionary* inputOptions = NULL;
    AVFormatContext* inputFormatContext = NULL;
    AVPacket* inputPacket = NULL;
    
    // "mono2abs" and "abs" causes a memory leak ("default" does not leak)
    ret = av_dict_set(&inputOptions, "timestamps", "mono2abs", 0);
    if (ret < 0) {
        fprintf(stderr, "Failed to set v4l2 'timestamp' option");
        goto end;
    }
    
    avdevice_register_all();
    
    const AVInputFormat* inputFormat = av_find_input_format("v4l2");
    if (!inputFormat) {
        fprintf(stderr, "Failed to find input format");
        ret = -1;
        goto end;
    }
    
    inputFormatContext = avformat_alloc_context();
    if (!inputFormatContext) {
        fprintf(stderr, "Failed to allocate input format context");
        ret = AVERROR(ENOMEM);
        goto end;
    }
    
    ret = avformat_open_input(&inputFormatContext, "/dev/video0", inputFormat, &inputOptions);
    if (ret < 0) {
        fprintf(stderr, "Failed to open input device");
        goto end;
    }
    
    ret = avformat_find_stream_info(inputFormatContext, NULL);
    if (ret < 0) {
        fprintf(stderr, "Failed to find input stream info");
        goto end;
    }
    
    av_dump_format(inputFormatContext, 0, "/dev/video0", 0);
    
    inputPacket = av_packet_alloc();
    if (!inputPacket) {
        fprintf(stderr, "Failed to allocate input packet");
        ret = AVERROR(ENOMEM);
        goto end;
    }
    
    // read at least one frame to avoid this error on closing: "ioctl(VIDIOC_QBUF): Bad file descriptor"
    ret = av_read_frame(inputFormatContext, inputPacket);
    if (ret < 0) {
        fprintf(stderr, "Failed to read input packet");
        goto end;
    }
    
    ret = 0;
    
end:
    if (inputPacket)
        av_packet_free(&inputPacket);
    
    if (inputFormatContext)
        avformat_close_input(&inputFormatContext);
    
    if (inputOptions)
        av_dict_free(&inputOptions);
    
    return ret;
}

Compiled with:

$ gcc v4l2_mem_leak.c -o v4l2_mem_leak -g -Wall -Wextra -pedantic -fsanitize=address -fno-omit-frame-pointer -lavdevice -lavformat -lavutil -lavcodec

Output:

$ ./v4l2_mem_leak 
[video4linux2,v4l2 @ 0x617000002000] Detected monotonic timestamps, converting
Input #0, video4linux2,v4l2, from '/dev/video0':
  Duration: N/A, start: 1658787218.575150, bitrate: 110592 kb/s
  Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 640x480, 110592 kb/s, 30 fps, 30 tbr, 1000k tbn

=================================================================
==5506==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 40 byte(s) in 1 object(s) allocated from:
    #0 0x7f90b0ebefc7 in __interceptor_posix_memalign /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:145
    #1 0x7f90b064fdb5 in av_malloc (/usr/lib/libavutil.so.57+0x4fdb5)

SUMMARY: AddressSanitizer: 40 byte(s) leaked in 1 allocation(s).

Compiler is gcc 12.1.0.

[quinkblack]

Could you help testing the following patch?

​http://ffmpeg.org/pipermail/ffmpeg-devel/2022-July/299334.html

[bermond]

I can confirm that applying the patch on top of git master fixes this memory leak. Using 'mono2abs' and 'abs' values does not leak anymore with it.

I'm using an android phone with droidcam as the camera device.

Thank you for working on this!

[bermond]

This is now fixed on the current git master by commit 30aa0c3f4873a92c5e3da8ba8cf030de56bf4cf7.

Thanks to everyone involved.