From d415da7ae571c3854550564a1764e763cc83c921 Mon Sep 17 00:00:00 2001
From: ellie timoney <ellie@fastmail.com>
Date: Wed, 19 May 2021 13:39:34 +1000
Subject: [PATCH] strhash: replace ad-hoc algorithm with seeded djb2

Part of CVE-2021-33582
---
 lib/strhash.c | 37 ++++++++++++++++++++++++++-----------
 lib/strhash.h |  6 +++++-
 2 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/lib/strhash.c b/lib/strhash.c
index 3457abab27..8f68d13867 100644
--- a/lib/strhash.c
+++ b/lib/strhash.c
@@ -57,17 +57,32 @@
 #include "assert.h"
 #include "strhash.h"
 
-unsigned strhash(const char *string)
+#include "lib/strhash.h"
+
+/* The well-known djb2 algorithm (e.g. http://www.cse.yorku.ca/~oz/hash.html),
+ * with the addition of an optional seed to limit predictability.
+ *
+ * XXX return type 'unsigned' for back-compat to previous version, but
+ * XXX ought to be 'uint32_t'
+ */
+unsigned strhash_seeded_djb2(uint32_t seed, const char *string)
 {
-      unsigned ret_val = 0;
-      int i;
+    const unsigned char *ustr = (const unsigned char *) string;
+    unsigned hash = 5381;
+    int c;
+
+    if (seed) {
+        /* treat the bytes of the seed as a prefix to the string */
+        unsigned i;
+        for (i = 0; i < sizeof seed; i++) {
+            c = seed & 0xff;
+            hash = ((hash << 5) + hash) ^ c;
+            seed >>= 8;
+        }
+    }
+
+    while ((c = *ustr++))
+        hash = ((hash << 5) + hash) ^ c;
 
-      while (*string)
-      {
-            i = (int) *string;
-            ret_val ^= i;
-            ret_val <<= 1;
-            string ++;
-      }
-      return ret_val;
+    return hash;
 }
diff --git a/lib/strhash.h b/lib/strhash.h
index 3ecb432a34..dc6f6b759f 100644
--- a/lib/strhash.h
+++ b/lib/strhash.h
@@ -43,6 +43,7 @@
  */
 
 #ifndef _STRHASH_H_
+#include <stdint.h>
 
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
@@ -57,6 +58,9 @@
 #include <syslog.h>
 #include <errno.h>
 
-unsigned strhash(const char *string);
+unsigned strhash_seeded_djb2(uint32_t seed, const char *string);
+
+#define strhash(in)             strhash_seeded_djb2((0),  (in))
+#define strhash_seeded(sd, in)  strhash_seeded_djb2((sd), (in))
 
 #endif /* _STRHASH_H_ */