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.
The highlighted line of code below is the trigger point of this particular Fedora 23 race weakness.
_GL_CXXALIAS_RPL (read, ssize_t, (int fd, void *buf, size_t count)); # else /* Need to cast, because on mingw, the third parameter is unsigned int count and the return type is 'int'. */ _GL_CXXALIAS_SYS_CAST (read, ssize_t, (int fd, void *buf, size_t count)); # endif _GL_CXXALIASWARN (read); #endif #if @GNULIB_READLINK@ /* Read the contents of the symbolic link FILE and place the first BUFSIZE bytes of it into BUF. Return the number of bytes placed into BUF if successful, otherwise -1 and errno set. See the POSIX:2008 specification <http://pubs.opengroup.org/onlinepubs/9699919799/functions/readlink.html>. */ # if @REPLACE_READLINK@ # if !(defined __cplusplus && defined GNULIB_NAMESPACE) # define readlink rpl_readlink # endif _GL_FUNCDECL_RPL (readlink, ssize_t, (const char *file, char *buf, size_t bufsize) _GL_ARG_NONNULL ((1, 2))); _GL_CXXALIAS_RPL (readlink, ssize_t, (const char *file, char *buf, size_t bufsize)); # else # if !@HAVE_READLINK@ _GL_FUNCDECL_SYS (readlink, ssize_t, (const char *file, char *buf, size_t bufsize) _GL_ARG_NONNULL ((1, 2))); # endif _GL_CXXALIAS_SYS (readlink, ssize_t, (const char *file, char *buf, size_t bufsize)); # endif _GL_CXXALIASWARN (readlink); #elif defined GNULIB_POSIXCHECK # undef readlink # if HAVE_RAW_DECL_READLINK _GL_WARN_ON_USE (readlink, "readlink is unportable - " "use gnulib module readlink for portability"); # endif #endif #if @GNULIB_READLINKAT@ # if @REPLACE_READLINKAT@ # if !(defined __cplusplus && defined GNULIB_NAMESPACE) # define readlinkat rpl_readlinkat # endif