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/* vi: set sw=4 ts=4: */
/*
* update_passwd
*
* update_passwd is a common function for passwd and chpasswd applets;
* it is responsible for updating password file (i.e. /etc/passwd or
* /etc/shadow) for a given user and password.
*
* Moved from loginutils/passwd.c by Alexander Shishkin <virtuoso@slind.org>
*/
#include "libbb.h"
#if ENABLE_SELINUX
static void check_selinux_update_passwd(const char *username)
{
security_context_t context;
char *seuser;
if (getuid() != (uid_t)0 || is_selinux_enabled() == 0)
return; /* No need to check */
if (getprevcon_raw(&context) < 0)
bb_perror_msg_and_die("getprevcon failed");
seuser = strtok(context, ":");
if (!seuser)
bb_error_msg_and_die("invalid context '%s'", context);
if (strcmp(seuser, username) != 0) {
if (checkPasswdAccess(PASSWD__PASSWD) != 0)
bb_error_msg_and_die("SELinux: access denied");
}
if (ENABLE_FEATURE_CLEAN_UP)
freecon(context);
}
#else
#define check_selinux_update_passwd(username) ((void)0)
#endif
int update_passwd(const char *filename, const char *username,
const char *new_pw)
{
struct stat sb;
struct flock lock;
FILE *old_fp;
FILE *new_fp;
char *fnamesfx;
char *sfx_char;
unsigned user_len;
int old_fd;
int new_fd;
int i;
int cnt = 0;
int ret = -1; /* failure */
filename = xmalloc_follow_symlinks(filename);
if (filename == NULL)
return -1;
check_selinux_update_passwd(username);
/* New passwd file, "/etc/passwd+" for now */
fnamesfx = xasprintf("%s+", filename);
sfx_char = &fnamesfx[strlen(fnamesfx)-1];
username = xasprintf("%s:", username);
user_len = strlen(username);
old_fp = fopen(filename, "r+");
if (!old_fp)
goto free_mem;
old_fd = fileno(old_fp);
selinux_preserve_fcontext(old_fd);
/* Try to create "/etc/passwd+". Wait if it exists. */
i = 30;
do {
// FIXME: on last iteration try w/o O_EXCL but with O_TRUNC?
new_fd = open(fnamesfx, O_WRONLY|O_CREAT|O_EXCL, 0600);
if (new_fd >= 0) goto created;
if (errno != EEXIST) break;
usleep(100000); /* 0.1 sec */
} while (--i);
bb_perror_msg("cannot create '%s'", fnamesfx);
goto close_old_fp;
created:
if (!fstat(old_fd, &sb)) {
fchmod(new_fd, sb.st_mode & 0777); /* ignore errors */
fchown(new_fd, sb.st_uid, sb.st_gid);
}
new_fp = fdopen(new_fd, "w");
if (!new_fp) {
close(new_fd);
goto unlink_new;
}
/* Backup file is "/etc/passwd-" */
*sfx_char = '-';
/* Delete old backup */
i = (unlink(fnamesfx) && errno != ENOENT);
/* Create backup as a hardlink to current */
if (i || link(filename, fnamesfx))
bb_perror_msg("warning: cannot create backup copy '%s'", fnamesfx);
*sfx_char = '+';
/* Lock the password file before updating */
lock.l_type = F_WRLCK;
lock.l_whence = SEEK_SET;
lock.l_start = 0;
lock.l_len = 0;
if (fcntl(old_fd, F_SETLK, &lock) < 0)
bb_perror_msg("warning: cannot lock '%s'", filename);
lock.l_type = F_UNLCK;
/* Read current password file, write updated /etc/passwd+ */
while (1) {
char *line = xmalloc_fgets(old_fp);
if (!line) break; /* EOF/error */
if (strncmp(username, line, user_len) == 0) {
/* we have a match with "username:"... */
const char *cp = line + user_len;
/* now cp -> old passwd, skip it: */
cp = strchrnul(cp, ':');
/* now cp -> ':' after old passwd or -> "" */
fprintf(new_fp, "%s%s%s", username, new_pw, cp);
cnt++;
} else
fputs(line, new_fp);
free(line);
}
fcntl(old_fd, F_SETLK, &lock);
/* We do want all of them to execute, thus | instead of || */
if ((ferror(old_fp) | fflush(new_fp) | fsync(new_fd) | fclose(new_fp))
|| rename(fnamesfx, filename)
) {
/* At least one of those failed */
goto unlink_new;
}
ret = cnt; /* whee, success! */
unlink_new:
if (ret < 0) unlink(fnamesfx);
close_old_fp:
fclose(old_fp);
free_mem:
free(fnamesfx);
free((char *)filename);
free((char *)username);
return ret;
}
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