diff options
| -rw-r--r-- | dbutil.c | 13 | ||||
| -rw-r--r-- | dbutil.h | 3 | ||||
| -rw-r--r-- | packet.c | 2 | ||||
| -rw-r--r-- | svr-authpasswd.c | 13 |
4 files changed, 29 insertions, 2 deletions
@@ -884,3 +884,16 @@ int m_str_to_uint(const char* str, unsigned int *val) { return DROPBEAR_SUCCESS; } } + +int constant_time_memcmp(const void* a, const void *b, size_t n) +{ + const char *xa = a, *xb = b; + uint8_t c = 0; + size_t i; + for (i = 0; i < n; i++) + { + c |= (xa[i] ^ xb[i]); + } + return c; +} + @@ -94,4 +94,7 @@ int m_str_to_uint(const char* str, unsigned int *val); /* Dropbear assertion */ #define dropbear_assert(X) do { if (!(X)) { fail_assert(#X, __FILE__, __LINE__); } } while (0) +/* Returns 0 if a and b have the same contents */ +int constant_time_memcmp(const void* a, const void *b, size_t n); + #endif /* _DBUTIL_H_ */ @@ -376,7 +376,7 @@ static int checkmac() { /* compare the hash */ buf_setpos(ses.readbuf, contents_len); - if (memcmp(mac_bytes, buf_getptr(ses.readbuf, mac_size), mac_size) != 0) { + if (constant_time_memcmp(mac_bytes, buf_getptr(ses.readbuf, mac_size), mac_size) != 0) { return DROPBEAR_FAILURE; } else { return DROPBEAR_SUCCESS; diff --git a/svr-authpasswd.c b/svr-authpasswd.c index 17dd2a1..7a5a121 100644 --- a/svr-authpasswd.c +++ b/svr-authpasswd.c @@ -33,6 +33,17 @@ #ifdef ENABLE_SVR_PASSWORD_AUTH +static int constant_time_strcmp(const char* a, const char* b) { + size_t la = strlen(a); + size_t lb = strlen(b); + + if (la != lb) { + return 1; + } + + return constant_time_memcmp(a, b, la); +} + /* Process a password auth request, sending success or failure messages as * appropriate */ void svr_auth_password() { @@ -82,7 +93,7 @@ void svr_auth_password() { return; } - if (strcmp(testcrypt, passwdcrypt) == 0) { + if (constant_time_strcmp(testcrypt, passwdcrypt) == 0) { /* successful authentication */ dropbear_log(LOG_NOTICE, "Password auth succeeded for '%s' from %s", |