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.
This accepts filename arguments; if an attacker can move those files, a race condition results..
The highlighted line of code below is the trigger point of this particular Alpine 3.8 race weakness.
/* Change the owner of FILE to UID (if UID is not -1) and the group of FILE to GID (if GID is not -1). Follow symbolic links. Return 0 if successful, otherwise -1 and errno set. See the POSIX:2008 specification <http://pubs.opengroup.org/onlinepubs/9699919799/functions/chown.html. */ # if @REPLACE_CHOWN@ # if !(defined __cplusplus && defined GNULIB_NAMESPACE) # undef chown # define chown rpl_chown # endif _GL_FUNCDECL_RPL (chown, int, (const char *file, uid_t uid, gid_t gid) _GL_ARG_NONNULL ((1))); _GL_CXXALIAS_RPL (chown, int, (const char *file, uid_t uid, gid_t gid)); # else # if !@HAVE_CHOWN@ _GL_FUNCDECL_SYS (chown, int, (const char *file, uid_t uid, gid_t gid) _GL_ARG_NONNULL ((1))); # endif _GL_CXXALIAS_SYS (chown, int, (const char *file, uid_t uid, gid_t gid)); # endif _GL_CXXALIASWARN (chown); #elif defined GNULIB_POSIXCHECK # undef chown # if HAVE_RAW_DECL_CHOWN _GL_WARN_ON_USE (chown, "chown fails to follow symlinks on some systems and " "doesn't treat a uid or gid of -1 on some systems - " "use gnulib module chown for portability"); # endif #endif #if @GNULIB_CLOSE@ # if @REPLACE_CLOSE@ /* Automatically included by modules that need a replacement for close. */ # if !(defined __cplusplus && defined GNULIB_NAMESPACE) # undef close # define close rpl_close # endif _GL_FUNCDECL_RPL (close, int, (int fd)); _GL_CXXALIAS_RPL (close, int, (int fd)); # else _GL_CXXALIAS_SYS (close, int, (int fd)); # endif _GL_CXXALIASWARN (close); #elif @UNISTD_H_HAVE_WINSOCK2_H_AND_USE_SOCKETS@ # undef close # define close close_used_without_requesting_gnulib_module_close #elif defined GNULIB_POSIXCHECK # undef close /* Assume close is always declared. */