alsa-project/alsa-lib issue #461 was opened from harryrowe01:

Calling snd_pcm_hw_params_get_buffer_size is causing memory corruption in the calling program.

The following C program demonstrates the issue.

/*

This example opens the default PCM device, sets some parameters, and then displays the value of some of the hardware parameters. It does not perform any sound playback or recording.

*/

/* Use the newer ALSA API */ #define ALSA_PCM_NEW_HW_PARAMS_API

/* All of the ALSA library API is defined * in this header */ #include <alsa/asoundlib.h>

int main() { int rc; snd_pcm_t *handle; snd_pcm_hw_params_t *params, *save_params; unsigned int val, val2; int dir; snd_pcm_uframes_t frames;

/* Open PCM device for playback. */ rc = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0); if (rc < 0) { fprintf(stderr, "unable to open pcm device: %s\n", snd_strerror(rc)); exit(1); }

/* Allocate a hardware parameters object. */ snd_pcm_hw_params_alloca(&params);

/* Fill it in with default values. */ snd_pcm_hw_params_any(handle, params);

/* Set the desired hardware parameters. */

/* Interleaved mode */ snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);

/* Signed 16-bit little-endian format */ snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);

/* Two channels (stereo) */ snd_pcm_hw_params_set_channels(handle, params, 2);

/* 44100 bits/second sampling rate (CD quality) */ val = 44100; // val = 8000; snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);

/* Write the parameters to the driver */ rc = snd_pcm_hw_params(handle, params); if (rc < 0) { fprintf(stderr, "unable to set hw parameters: %s\n", snd_strerror(rc)); exit(1); }

/* Display information about the PCM interface */

// Before calling snd_pcm_hw_params_get_buffer_size, save // a copy of params which points to the parameter block. save_params = params;

// This call to snd_pcm_hw_params_get_buffer_size causes // the value of params in main to be corrupted. // Since the params argument to the function is passed // by value, the function itself should not have access to // the original variable in main.

snd_pcm_hw_params_get_buffer_size(params, (snd_pcm_uframes_t *)&val); // Then if the pointer has been modified, flag the problem and // restore the pointer from the saved value. if( params != save_params ) { printf( "The pointer to the parameter block has been corrupted!\n" ); printf( "was %lx \n", save_params ); printf( "is now %lx \n", params ); printf( "So I'm fixing it.\n" ); params = save_params; }

printf("buffer size = %u frames\n", val);

snd_pcm_close(handle);

return 0; }

Compiled and run as follows:

harry@idun:~/Documents/morse$ cc bad_alsa.c -lasound -o bad_alsa harry@idun:~/Documents/morse$ ./bad_alsa The pointer to the parameter block has been corrupted! was 7ffcd2011610 is now 7ffc00000000 So I'm fixing it. buffer size = 1048576 frames harry@idun:~/Documents/morse$ cc bad_alsa.c -lasound -o bad_alsa harry@idun:~/Documents/morse$ ./bad_alsa The pointer to the parameter block has been corrupted! was 7fffc7483030 is now 7fff00000000 So I'm fixing it. buffer size = 1048576 frames harry@idun:~/Documents/morse$

Host is an AMD64 version of Debian 12. Installed version of ALSA library is libasound2 1.2.8-1+b1

Issue URL : https://github.com/alsa-project/alsa-lib/issues/461 Repository URL: https://github.com/alsa-project/alsa-lib