[tor-commits] [tor/maint-0.4.5] Assert on _all_ failures from RAND_bytes().

[nickm at torproject.org]

commit c0aa9e0a1b1633d3b221199d516294e14a5db9c6
Author: Nick Mathewson <nickm at torproject.org>
Date:   Mon May 17 08:50:01 2021 -0400

    Assert on _all_ failures from RAND_bytes().
    
    Previously, we would detect errors from a missing RNG
    implementation, but not failures from the RNG code itself.
    
    Fortunately, it appears those failures do not happen in practice
    when Tor is using OpenSSL's default RNG implementation.  Fixes bug
    40390; bugfix on 0.2.8.1-alpha. This issue is also tracked as
    TROVE-2021-004. Reported by Jann Horn at Google's Project Zero.
---
 changes/ticket40390             | 8 ++++++++
 src/lib/crypt_ops/crypto_rand.c | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/changes/ticket40390 b/changes/ticket40390
new file mode 100644
index 0000000000..b56fa4d9da
--- /dev/null
+++ b/changes/ticket40390
@@ -0,0 +1,8 @@
+  o Major bugfixes (security, defense-in-depth):
+    - Detect a wider variety of failure conditions from the OpenSSL RNG
+      code. Previously, we would detect errors from a missing RNG
+      implementation, but not failures from the RNG code itself.
+      Fortunately, it appears those failures do not happen in practice
+      when Tor is using OpenSSL's default RNG implementation.
+      Fixes bug 40390; bugfix on 0.2.8.1-alpha. This issue is also tracked as
+      TROVE-2021-004. Reported by Jann Horn at Google's Project Zero.
diff --git a/src/lib/crypt_ops/crypto_rand.c b/src/lib/crypt_ops/crypto_rand.c
index 915fe0870d..206929d6b3 100644
--- a/src/lib/crypt_ops/crypto_rand.c
+++ b/src/lib/crypt_ops/crypto_rand.c
@@ -525,7 +525,7 @@ crypto_rand_unmocked(char *to, size_t n)
   /* We consider a PRNG failure non-survivable. Let's assert so that we get a
    * stack trace about where it happened.
    */
-  tor_assert(r >= 0);
+  tor_assert(r == 1);
 #endif
 }