Mitigate Baron SameEdit (CVE-2021-3156) vulnerability

fedora 25
race weakness #512


Weakness Breakdown


A race condition exists when parallel code accesses shared data without proper coordination. An attack that uses a race-condition weakness takes advantage of the unsafe data access to manipulate how one of the parallel sections of code reacts. Even though each process runs as intended, the outcome is unexpected. For example, consider a bank service that depends on an encryption key that it reads from a known location. An independent cryptography service is responsible for generating the key and placing it where the bank is expected to read it in a timely manner. If the bank and cryptography services do not coordinate with each other, then the bank may read a blank encryption key before cryptography writes the key to the location. This can effectively turn off all encryption for the bank without either service, or the administrator, knowing that something has gone wrong.

Warning code(s):

This accepts filename arguments; if an attacker can move those files or change the link content, a race condition results. Also, it does not terminate with ASCII NUL..

File Name:



The highlighted line of code below is the trigger point of this particular Fedora 25 race weakness.

    char *spot;
#if defined(__LINUX__) || defined(__FREEBSD__)
    char procfile[1024];
    char linkfile[1024];
    int linksize;

    /* First allow environment variable override */
    spot = SDL_getenv("SDL_VIDEO_X11_WMCLASS");
    if (spot) {
        return SDL_strdup(spot);

    /* Next look at the application's executable name */
#if defined(__LINUX__) || defined(__FREEBSD__)
#if defined(__LINUX__)
    SDL_snprintf(procfile, SDL_arraysize(procfile), "/proc/%d/exe", getpid());
#elif defined(__FREEBSD__)
    SDL_snprintf(procfile, SDL_arraysize(procfile), "/proc/%d/file",
#error Where can we find the executable name?
    linksize = readlink(procfile, linkfile, sizeof(linkfile) - 1);
    if (linksize > 0) {
        linkfile[linksize] = '\0';
        spot = SDL_strrchr(linkfile, '/');
        if (spot) {
            return SDL_strdup(spot + 1);
        } else {
            return SDL_strdup(linkfile);
#endif /* __LINUX__ || __FREEBSD__ */

    /* Finally use the default we've used forever */
    return SDL_strdup("SDL_App");

/* X11 driver bootstrap functions */

static int
    Display *display = NULL;
    if (SDL_X11_LoadSymbols()) {
        display = X11_XOpenDisplay(NULL);
        if (display != NULL) {

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