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openssh
openssh-7.2p2-prevent_timing_user_enumeration.p...
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File openssh-7.2p2-prevent_timing_user_enumeration.patch of Package openssh
# HG changeset patch # Parent 40ce0de74a0d8b8181862b237b693d938310527b Prevent user enumeration through password processing timing CVE-2016-6210 bsc#989363 non-PAM part: upstream commit: 9286875a73b2de7736b5e50692739d314cd8d9dc PAM part: upstream commit: 283b97ff33ea2c641161950849931bd578de6946 diff --git a/openssh-7.2p2/auth-pam.c b/openssh-7.2p2/auth-pam.c --- a/openssh-7.2p2/auth-pam.c +++ b/openssh-7.2p2/auth-pam.c @@ -227,17 +227,16 @@ static pam_handle_t *sshpam_handle = NUL static int sshpam_err = 0; static int sshpam_authenticated = 0; static int sshpam_session_open = 0; static int sshpam_cred_established = 0; static int sshpam_account_status = -1; static char **sshpam_env = NULL; static Authctxt *sshpam_authctxt = NULL; static const char *sshpam_password = NULL; -static char badpw[] = "\b\n\r\177INCORRECT"; /* Some PAM implementations don't implement this */ #ifndef HAVE_PAM_GETENVLIST static char ** pam_getenvlist(pam_handle_t *pamh) { /* * XXX - If necessary, we can still support envrionment passing @@ -807,22 +806,45 @@ sshpam_query(void *ctx, char **name, cha free(msg); ctxt->pam_done = -1; return (-1); } } return (-1); } +/* + * Returns a junk password of identical length to that the user supplied. + * Used to mitigate timing attacks against crypt(3)/PAM stacks that + * vary processing time in proportion to password length. + */ +static char * +fake_password(const char *wire_password) +{ + const char junk[] = "\b\n\r\177INCORRECT"; + char *ret = NULL; + size_t i, l = wire_password != NULL ? strlen(wire_password) : 0; + + if (l >= INT_MAX) + fatal("%s: password length too long: %zu", __func__, l); + + ret = xmalloc(l + 1); + for (i = 0; i < l; i++) + ret[i] = junk[i % (sizeof(junk) - 1)]; + ret[i] = '\0'; + return ret; +} + /* XXX - see also comment in auth-chall.c:verify_response */ static int sshpam_respond(void *ctx, u_int num, char **resp) { Buffer buffer; struct pam_ctxt *ctxt = ctx; + char *fake; debug2("PAM: %s entering, %u responses", __func__, num); switch (ctxt->pam_done) { case 1: sshpam_authenticated = 1; return (0); case 0: break; @@ -833,18 +855,21 @@ sshpam_respond(void *ctx, u_int num, cha error("PAM: expected one response, got %u", num); return (-1); } buffer_init(&buffer); if (sshpam_authctxt->valid && (sshpam_authctxt->pw->pw_uid != 0 || options.permit_root_login == PERMIT_YES)) buffer_put_cstring(&buffer, *resp); - else - buffer_put_cstring(&buffer, badpw); + else { + fake = fake_password(*resp); + buffer_put_cstring(&buffer, fake); + free(fake); + } if (ssh_msg_send(ctxt->pam_psock, PAM_AUTHTOK, &buffer) == -1) { buffer_free(&buffer); return (-1); } buffer_free(&buffer); return (1); } @@ -1178,41 +1203,43 @@ static struct pam_conv passwd_conv = { s /* * Attempt password authentication via PAM */ int sshpam_auth_passwd(Authctxt *authctxt, const char *password) { int flags = (options.permit_empty_passwd == 0 ? PAM_DISALLOW_NULL_AUTHTOK : 0); + char *fake = NULL; if (!options.use_pam || sshpam_handle == NULL) fatal("PAM: %s called when PAM disabled or failed to " "initialise.", __func__); sshpam_password = password; sshpam_authctxt = authctxt; /* * If the user logging in is invalid, or is root but is not permitted * by PermitRootLogin, use an invalid password to prevent leaking * information via timing (eg if the PAM config has a delay on fail). */ if (!authctxt->valid || (authctxt->pw->pw_uid == 0 && options.permit_root_login != PERMIT_YES)) - sshpam_password = badpw; + sshpam_password = fake = fake_password(password); sshpam_err = pam_set_item(sshpam_handle, PAM_CONV, (const void *)&passwd_conv); if (sshpam_err != PAM_SUCCESS) fatal("PAM: %s: failed to set PAM_CONV: %s", __func__, pam_strerror(sshpam_handle, sshpam_err)); sshpam_err = pam_authenticate(sshpam_handle, flags); sshpam_password = NULL; + free(fake); if (sshpam_err == PAM_SUCCESS && authctxt->valid) { debug("PAM: password authentication accepted for %.100s", authctxt->user); return 1; } else { debug("PAM: password authentication failed for %.100s: %s", authctxt->valid ? authctxt->user : "an illegal user", pam_strerror(sshpam_handle, sshpam_err)); diff --git a/openssh-7.2p2/auth-passwd.c b/openssh-7.2p2/auth-passwd.c --- a/openssh-7.2p2/auth-passwd.c +++ b/openssh-7.2p2/auth-passwd.c @@ -188,28 +188,32 @@ sys_auth_passwd(Authctxt *authctxt, cons return (auth_close(as)); } } #elif !defined(CUSTOM_SYS_AUTH_PASSWD) int sys_auth_passwd(Authctxt *authctxt, const char *password) { struct passwd *pw = authctxt->pw; - char *encrypted_password; + char *encrypted_password, *salt = NULL; /* Just use the supplied fake password if authctxt is invalid */ char *pw_password = authctxt->valid ? shadow_pw(pw) : pw->pw_passwd; /* Check for users with no password. */ if (strcmp(pw_password, "") == 0 && strcmp(password, "") == 0) return (1); - /* Encrypt the candidate password using the proper salt. */ - encrypted_password = xcrypt(password, - (pw_password[0] && pw_password[1]) ? pw_password : "xx"); + /* + * Encrypt the candidate password using the proper salt, or pass a + * NULL and let xcrypt pick one. + */ + if (authctxt->valid && pw_password[0] && pw_password[1]) + salt = pw_password; + encrypted_password = xcrypt(password, salt); /* * Authentication is accepted if the encrypted passwords * are identical. */ return encrypted_password != NULL && strcmp(encrypted_password, pw_password) == 0; } diff --git a/openssh-7.2p2/openbsd-compat/xcrypt.c b/openssh-7.2p2/openbsd-compat/xcrypt.c --- a/openssh-7.2p2/openbsd-compat/xcrypt.c +++ b/openssh-7.2p2/openbsd-compat/xcrypt.c @@ -20,16 +20,17 @@ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include "includes.h" #include <sys/types.h> +#include <string.h> #include <unistd.h> #include <pwd.h> # if defined(HAVE_CRYPT_H) && !defined(HAVE_SECUREWARE) # include <crypt.h> # endif # ifdef __hpux @@ -57,21 +58,54 @@ # include "md5crypt.h" # endif # if defined(WITH_OPENSSL) && !defined(HAVE_CRYPT) && defined(HAVE_DES_CRYPT) # include <openssl/des.h> # define crypt DES_crypt # endif +/* + * Pick an appropriate password encryption type and salt for the running + * system. + */ +static const char * +pick_salt(void) +{ + struct passwd *pw; + char *passwd, *p; + size_t typelen; + static char salt[32]; + + if (salt[0] != '\0') + return salt; + strlcpy(salt, "xx", sizeof(salt)); + if ((pw = getpwuid(0)) == NULL) + return salt; + passwd = shadow_pw(pw); + if (passwd[0] != '$' || (p = strrchr(passwd + 1, '$')) == NULL) + return salt; /* no $, DES */ + typelen = p - passwd + 1; + strlcpy(salt, passwd, MIN(typelen, sizeof(salt))); + explicit_bzero(passwd, strlen(passwd)); + return salt; +} + char * xcrypt(const char *password, const char *salt) { char *crypted; + /* + * If we don't have a salt we are encrypting a fake password for + * for timing purposes. Pick an appropriate salt. + */ + if (salt == NULL) + salt = pick_salt(); + # ifdef HAVE_MD5_PASSWORDS if (is_md5_salt(salt)) crypted = md5_crypt(password, salt); else crypted = crypt(password, salt); # elif defined(__hpux) && !defined(HAVE_SECUREWARE) if (iscomsec()) crypted = bigcrypt(password, salt);
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