centos 7
race weakness #30

5

Weakness Breakdown


Definition:

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:

libdrm-2.4.91/xf86drm.c

Context:

The highlighted line of code below is the trigger point of this particular Centos 7 race weakness.

             value = strndup(start, end - start);
            break;
        }
    }

    free(line);
    fclose(fp);

    free(key);

    return value;
}
#endif

static int drmParseSubsystemType(int maj, int min)
{
#ifdef __linux__
    char path[PATH_MAX + 1];
    char link[PATH_MAX + 1] = "";
    char *name;

    snprintf(path, PATH_MAX, "/sys/dev/char/%d:%d/device/subsystem",
             maj, min);

    if (readlink(path, link, PATH_MAX) < 0)
        return -errno;

    name = strrchr(link, '/');
    if (!name)
        return -EINVAL;

    if (strncmp(name, "/pci", 4) == 0)
        return DRM_BUS_PCI;

    if (strncmp(name, "/usb", 4) == 0)
        return DRM_BUS_USB;

    if (strncmp(name, "/platform", 9) == 0)
        return DRM_BUS_PLATFORM;

    if (strncmp(name, "/host1x", 7) == 0)
        return DRM_BUS_HOST1X;

    return -EINVAL;
#elif defined(__OpenBSD__)
    return DRM_BUS_PCI;
#else
#warning "Missing implementation of drmParseSubsystemType"
    return -EINVAL;
#endif 

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