fedora 25
race weakness #521

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, a race condition results..

File Name:

busybox-1.22.1/archival/rpm.c

Context:

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

 {
	struct stat oldfile;
	int stat_res;
	char *newname;
	if (rpm_getint(TAG_FILEFLAGS, fileref) & RPMFILE_CONFIG) {
		/* Only need to backup config files */
		stat_res = lstat(filename, &oldfile);
		if (stat_res == 0 && S_ISREG(oldfile.st_mode)) {
			/* File already exists  - really should check MD5's etc to see if different */
			newname = xasprintf("%s.rpmorig", filename);
			copy_file(filename, newname, FILEUTILS_RECUR | FILEUTILS_PRESERVE_STATUS);
			remove_file(filename, FILEUTILS_RECUR | FILEUTILS_FORCE);
			free(newname);
		}
	}
}

static void fileaction_setowngrp(char *filename, int fileref)
{
	/* real rpm warns: "user foo does not exist - using <you>" */
	struct passwd *pw = getpwnam(rpm_getstr(TAG_FILEUSERNAME, fileref));
	int uid = pw ? pw->pw_uid : getuid(); /* or euid? */
	struct group *gr = getgrnam(rpm_getstr(TAG_FILEGROUPNAME, fileref));
	int gid = gr ? gr->gr_gid : getgid();
	chown(filename, uid, gid);
}

static void loop_through_files(int filetag, void (*fileaction)(char *filename, int fileref))
{
	int count = 0;
	while (rpm_getstr(filetag, count)) {
		char* filename = xasprintf("%s%s",
			rpm_getstr(TAG_DIRNAMES, rpm_getint(TAG_DIRINDEXES, count)),
			rpm_getstr(TAG_BASENAMES, count));
		fileaction(filename, count++);
		free(filename);
	}
}

int rpm_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int rpm_main(int argc, char **argv)
{
	int opt, func = 0;
	const unsigned pagesize = getpagesize();

	while ((opt = getopt(argc, argv, "iqpldc")) != -1) {
		switch (opt) {
		case 'i': /* First arg: Install mode, with q: Information */
			if (!func) func = rpm_install;
			else func |= rpm_query_info; 

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