From 8f6ce7fb090a674f18b72e89a2b868fe1343fe8f Mon Sep 17 00:00:00 2001 From: Dean Rasheed Date: Fri, 20 Jul 2018 08:55:44 +0100 Subject: [PATCH] Guard against rare RAND_bytes() failures in pg_strong_random(). When built using OpenSSL, pg_strong_random() uses RAND_bytes() to generate the random number. On very rare occasions that can fail, if its PRNG has not been seeded with enough data. Additionally, once it does fail, all subsequent calls will also fail until more seed data is added. Since this is required during backend startup, this can result in all new backends failing to start until a postmaster restart. Guard against that by checking the state of OpenSSL's PRNG using RAND_status(), and if necessary (very rarely), seeding it using RAND_poll(). Back-patch to v10, where pg_strong_random() was introduced. Dean Rasheed and Michael Paquier. Discussion: https://postgr.es/m/CAEZATCXMtxbzSAvyKKk5uCRf9pNt4UV%2BF_5v%3DgLfJUuPxU4Ytg%40mail.gmail.com --- src/port/pg_strong_random.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/src/port/pg_strong_random.c b/src/port/pg_strong_random.c index bc7a8aacb9..f9a06d6606 100644 --- a/src/port/pg_strong_random.c +++ b/src/port/pg_strong_random.c @@ -103,6 +103,35 @@ pg_strong_random(void *buf, size_t len) * When built with OpenSSL, use OpenSSL's RAND_bytes function. */ #if defined(USE_OPENSSL_RANDOM) + int i; + + /* + * Check that OpenSSL's CSPRNG has been sufficiently seeded, and if not + * add more seed data using RAND_poll(). With some older versions of + * OpenSSL, it may be necessary to call RAND_poll() a number of times. + */ +#define NUM_RAND_POLL_RETRIES 8 + + for (i = 0; i < NUM_RAND_POLL_RETRIES; i++) + { + if (RAND_status() == 1) + { + /* The CSPRNG is sufficiently seeded */ + break; + } + + if (RAND_poll() == 0) + { + /* + * RAND_poll() failed to generate any seed data, which means that + * RAND_bytes() will probably fail. For now, just fall through + * and let that happen. XXX: maybe we could seed it some other + * way. + */ + break; + } + } + if (RAND_bytes(buf, len) == 1) return true; return false; -- 2.40.0