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factor out common PRNG reseed before privdrop 

Add a call to RAND_poll() to ensure than more than pid+time gets
stirred into child processes states. Prompted by analysis from Jann
Horn at Project Zero. ok dtucker@
This commit is contained in:
Damien Miller 2016-11-30 13:51:49 +11:00
parent 79e4829ec8
commit c9f880c195
1 changed files with 23 additions and 19 deletions
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42
sshd.c
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@ -499,9 +499,29 @@ demote_sensitive_data(void)
}
static void
privsep_preauth_child(void)
reseed_prngs(void)
{
u_int32_t rnd[256];
#ifdef WITH_OPENSSL
RAND_poll();
#endif
arc4random_stir(); /* noop on recent arc4random() implementations */
arc4random_buf(rnd, sizeof(rnd)); /* let arc4random notice PID change */
#ifdef WITH_OPENSSL
RAND_seed(rnd, sizeof(rnd));
/* give libcrypto a chance to notice the PID change */
if ((RAND_bytes((u_char *)rnd, 1)) != 1)
fatal("%s: RAND_bytes failed", __func__);
#endif
explicit_bzero(rnd, sizeof(rnd));
}
static void
privsep_preauth_child(void)
{
gid_t gidset[1];
/* Enable challenge-response authentication for privilege separation */
@ -513,14 +533,7 @@ privsep_preauth_child(void)
ssh_gssapi_prepare_supported_oids();
#endif
arc4random_stir();
arc4random_buf(rnd, sizeof(rnd));
#ifdef WITH_OPENSSL
RAND_seed(rnd, sizeof(rnd));
if ((RAND_bytes((u_char *)rnd, 1)) != 1)
fatal("%s: RAND_bytes failed", __func__);
#endif
explicit_bzero(rnd, sizeof(rnd));
reseed_prngs();
/* Demote the private keys to public keys. */
demote_sensitive_data();
@ -616,8 +629,6 @@ privsep_preauth(Authctxt *authctxt)
static void
privsep_postauth(Authctxt *authctxt)
{
u_int32_t rnd[256];
#ifdef DISABLE_FD_PASSING
if (1) {
#else
@ -651,14 +662,7 @@ privsep_postauth(Authctxt *authctxt)
/* Demote the private keys to public keys. */
demote_sensitive_data();
arc4random_stir();
arc4random_buf(rnd, sizeof(rnd));
#ifdef WITH_OPENSSL
RAND_seed(rnd, sizeof(rnd));
if ((RAND_bytes((u_char *)rnd, 1)) != 1)
fatal("%s: RAND_bytes failed", __func__);
#endif
explicit_bzero(rnd, sizeof(rnd));
reseed_prngs();
/* Drop privileges */
do_setusercontext(authctxt->pw);