diff options
author | Emilia Kasper <emilia@openssl.org> | 2016-02-24 12:59:59 +0100 |
---|---|---|
committer | Emilia Kasper <emilia@openssl.org> | 2016-02-25 15:42:48 +0100 |
commit | 380f18ed5f140e0ae1b68f3ab8f4f7c395658d9e (patch) | |
tree | 83e686e480f176176595a3b2f388be366b774b08 /crypto/srp | |
parent | 37529928faa8456e85a9c5ad9255517da8dd0c61 (diff) |
CVE-2016-0798: avoid memory leak in SRP
The SRP user database lookup method SRP_VBASE_get_by_user had confusing
memory management semantics; the returned pointer was sometimes newly
allocated, and sometimes owned by the callee. The calling code has no
way of distinguishing these two cases.
Specifically, SRP servers that configure a secret seed to hide valid
login information are vulnerable to a memory leak: an attacker
connecting with an invalid username can cause a memory leak of around
300 bytes per connection.
Servers that do not configure SRP, or configure SRP but do not configure
a seed are not vulnerable.
In Apache, the seed directive is known as SSLSRPUnknownUserSeed.
To mitigate the memory leak, the seed handling in SRP_VBASE_get_by_user
is now disabled even if the user has configured a seed.
Applications are advised to migrate to SRP_VBASE_get1_by_user. However,
note that OpenSSL makes no strong guarantees about the
indistinguishability of valid and invalid logins. In particular,
computations are currently not carried out in constant time.
Reviewed-by: Rich Salz <rsalz@openssl.org>
Diffstat (limited to 'crypto/srp')
-rw-r--r-- | crypto/srp/srp_vfy.c | 58 |
1 files changed, 53 insertions, 5 deletions
diff --git a/crypto/srp/srp_vfy.c b/crypto/srp/srp_vfy.c index 0a9de14011..0d3da7ef17 100644 --- a/crypto/srp/srp_vfy.c +++ b/crypto/srp/srp_vfy.c @@ -184,7 +184,7 @@ static char *t_tob64(char *dst, const unsigned char *src, int size) return olddst; } -static void SRP_user_pwd_free(SRP_user_pwd *user_pwd) +void SRP_user_pwd_free(SRP_user_pwd *user_pwd) { if (user_pwd == NULL) return; @@ -246,6 +246,24 @@ static int SRP_user_pwd_set_sv_BN(SRP_user_pwd *vinfo, BIGNUM *s, BIGNUM *v) return (vinfo->s != NULL && vinfo->v != NULL); } +static SRP_user_pwd *srp_user_pwd_dup(SRP_user_pwd *src) +{ + SRP_user_pwd *ret; + + if (src == NULL) + return NULL; + if ((ret = SRP_user_pwd_new()) == NULL) + return NULL; + + SRP_user_pwd_set_gN(ret, src->g, src->N); + if (!SRP_user_pwd_set_ids(ret, src->id, src->info) + || !SRP_user_pwd_set_sv_BN(ret, BN_dup(src->s), BN_dup(src->v))) { + SRP_user_pwd_free(ret); + return NULL; + } + return ret; +} + SRP_VBASE *SRP_VBASE_new(char *seed_key) { SRP_VBASE *vb = OPENSSL_malloc(sizeof(*vb)); @@ -467,21 +485,51 @@ int SRP_VBASE_init(SRP_VBASE *vb, char *verifier_file) } -SRP_user_pwd *SRP_VBASE_get_by_user(SRP_VBASE *vb, char *username) +static SRP_user_pwd *find_user(SRP_VBASE *vb, char *username) { int i; SRP_user_pwd *user; - unsigned char digv[SHA_DIGEST_LENGTH]; - unsigned char digs[SHA_DIGEST_LENGTH]; - EVP_MD_CTX *ctxt = NULL; if (vb == NULL) return NULL; + for (i = 0; i < sk_SRP_user_pwd_num(vb->users_pwd); i++) { user = sk_SRP_user_pwd_value(vb->users_pwd, i); if (strcmp(user->id, username) == 0) return user; } + + return NULL; +} + +/* + * DEPRECATED: use SRP_VBASE_get1_by_user instead. + * This method ignores the configured seed and fails for an unknown user. + * Ownership of the returned pointer is not released to the caller. + * In other words, caller must not free the result. + */ +SRP_user_pwd *SRP_VBASE_get_by_user(SRP_VBASE *vb, char *username) +{ + return find_user(vb, username); +} + +/* + * Ownership of the returned pointer is released to the caller. + * In other words, caller must free the result once done. + */ +SRP_user_pwd *SRP_VBASE_get1_by_user(SRP_VBASE *vb, char *username) +{ + SRP_user_pwd *user; + unsigned char digv[SHA_DIGEST_LENGTH]; + unsigned char digs[SHA_DIGEST_LENGTH]; + EVP_MD_CTX *ctxt = NULL; + + if (vb == NULL) + return NULL; + + if ((user = find_user(vb, username)) != NULL) + return srp_user_pwd_dup(user); + if ((vb->seed_key == NULL) || (vb->default_g == NULL) || (vb->default_N == NULL)) return NULL; |