pumpitupdev_pumptools/src/main/hook/patch/asound-fix.c

#define LOG_MODULE "patch-asound-fix"

#include <errno.h>
#include <grp.h>

#include "capnhook/hook/lib.h"

#include "util/log.h"
#include "util/mem.h"
#include "util/str.h"

typedef int (*getgrnam_r_t)(const char *name, struct group *grp, char *buf, size_t buflen, struct group **result);

static getgrnam_r_t patch_asound_fix_real_getgrnam_r;

static char** patch_asound_fix_split_user_list_str(const char* user_list_str)
{
    char* user_list_str_cpy = util_str_dup(user_list_str);
    char** user_list = util_xmalloc(sizeof(char*));
    size_t len_list = 1;

    char* ptr = strtok(user_list_str_cpy, ",");

    while (ptr != NULL) {
        // last token will likely read beyond newline to next : token for next group entry
        char* new_line_char = strstr(ptr, "\n");

        if (new_line_char) {
            *new_line_char = '\0';
        }

        len_list++;
        user_list = util_xrealloc(user_list, len_list * sizeof(char*));

        user_list[len_list - 2] = util_str_dup(ptr);
        user_list[len_list - 1] = NULL;

        ptr = strtok(NULL, ",");
    }

    free(user_list_str_cpy);

    return user_list;
}

static char* patch_asound_fix_user_list_to_str(char** user_list)
{
    char** ptr = user_list;
    char* str = util_str_dup("\0");

    while (*ptr != NULL) {
        char* mrg = util_str_merge(str, *ptr);
        free(str);
        str = util_str_merge(mrg, ",");
        free(mrg);

        ptr++;
    }

    return str;
}

int getgrnam_r(const char *name, struct group *grp, char *buf, size_t buflen, struct group **result)
{
    if (!patch_asound_fix_real_getgrnam_r) {
        patch_asound_fix_real_getgrnam_r = (getgrnam_r_t) cnh_lib_get_func_addr("getgrnam_r");
    }

    // We expect to use the standard "audio" group here, otherwise detection of this is not possible. Intercept
    // and execute the following re-implementation of the reading logic from file. I don't know if getgrnam_r usually
    // reads from a cached version of /etc/group but I suppose that doesn't matter here.
    if (!strcmp(name, "audio")) {
        log_debug("Trapping getgrnam_r for audio group of libasound");

        FILE* file = fopen("/etc/group", "r");

        fseek(file, 0, SEEK_END);
        size_t file_size = ftell(file);
        fseek(file, 0, SEEK_SET);

        char* buffer = (char*) util_xmalloc(file_size);

        if (fread(buffer, file_size, 1, file) != 1) {
            log_error("Reading /etc/group file failed: %s", strerror(errno));
            free(buffer);
            *result = NULL;
            return -1;
        }

        char* str_audio_pos = strstr(buffer, name);

        if (str_audio_pos == NULL) {
            log_error("Could not find 'audio' group in /etc/group required by libasound likely for defaults.pcm.ipc_gid"
                " from asound.conf. Make sure the group exists.");
            free(buffer);
            *result = NULL;
            return -1;
        }

        char* tok = strtok(str_audio_pos, ":");
        uint8_t cnt = 0;

        while (tok != NULL) {
            switch (cnt) {
                case 0:
                    grp->gr_name = util_str_dup(tok);
                    break;

                case 1:
                    grp->gr_passwd = util_str_dup(tok);
                    break;

                case 2:
                    grp->gr_gid = strtol(tok, NULL, 10);
                    break;

                case 3:
                    grp->gr_mem = patch_asound_fix_split_user_list_str(tok);
                    break;

                default:
                    log_error("audio group entry format in /etc/group invalid. Check your /etc/group file!");
                    free(buffer);
                    *result = NULL;
                    return -1;
            }

            cnt++;
            tok = strtok(NULL, ":");
        }

        char* grp_mem_str = patch_asound_fix_user_list_to_str(grp->gr_mem);
        log_debug("Resulting group struct: %s %s %d %s", grp->gr_name, grp->gr_passwd, grp->gr_gid, grp_mem_str);
        free(grp_mem_str);

        *result = grp;

        return 0;
    }

    return patch_asound_fix_real_getgrnam_r(name, grp, buf, buflen, result);
}

void patch_asound_fix_init()
{
    log_info("Initialized");
}