From: Hugo Landau <hlandau@openssl.org>
Date: Wed, 18 Jan 2023 15:43:56 +0000 (+0000)
Subject: Fix corruption when searching for CRLs in hashed directories (1.1)
X-Git-Tag: OpenSSL_1_1_1t~11
X-Git-Url: https://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff_plain;h=44da71693cdad2deb6430a47d3f3ee9f57065091

Fix corruption when searching for CRLs in hashed directories (1.1)

The by_dir certificate/CRL lookup code uses an OPENSSL_STACK to track
how many sequentially numbered CRL files have been loaded for a given
X509_NAME hash which is being requested. This avoids loading already
loaded CRL files and repeated stat() calls.

This OPENSSL_STACK is searched using sk_find, however this mutates
the OPENSSL_STACK unless it is known to be sorted. This operation
therefore requires a write lock, which was not taken.

Fix this issue by sorting the OPENSSL_STACK whenever it is mutated. This
guarantees no mutation will occur during sk_find. This is chosen over
taking a write lock during sk_find as retrieving a CRL by X509_NAME is
assumed to be a hotter path than the case where a new CRL is installed.

Also optimise the code by avoiding creating the structure to track the
last CRL file sequence number in the circumstance where it would match
the initial value, namely where no CRL with the given hash is installed.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20127)
---

diff --git a/crypto/x509/by_dir.c b/crypto/x509/by_dir.c
index 238c2519a6..cc9556f7b0 100644
--- a/crypto/x509/by_dir.c
+++ b/crypto/x509/by_dir.c
@@ -332,9 +332,13 @@ static int get_cert_by_subject(X509_LOOKUP *xl, X509_LOOKUP_TYPE type,
         tmp = sk_X509_OBJECT_value(xl->store_ctx->objs, j);
         X509_STORE_unlock(xl->store_ctx);
 
-        /* If a CRL, update the last file suffix added for this */
-
-        if (type == X509_LU_CRL) {
+        /*
+         * If a CRL, update the last file suffix added for this.
+         * We don't need to add an entry if k is 0 as this is the initial value.
+         * This avoids the need for a write lock and sort operation in the
+         * simple case where no CRL is present for a hash.
+         */
+        if (type == X509_LU_CRL && k > 0) {
             CRYPTO_THREAD_write_lock(ctx->lock);
             /*
              * Look for entry again in case another thread added an entry
@@ -362,6 +366,12 @@ static int get_cert_by_subject(X509_LOOKUP *xl, X509_LOOKUP_TYPE type,
                     ok = 0;
                     goto finish;
                 }
+
+                /*
+                 * Ensure stack is sorted so that subsequent sk_BY_DIR_HASH_find
+                 * will not mutate the stack and therefore require a write lock.
+                 */
+                sk_BY_DIR_HASH_sort(ent->hashes);
             } else if (hent->suffix < k) {
                 hent->suffix = k;
             }