From 12a26b8b34df23103d4da6d7e40705485266a4d6 Mon Sep 17 00:00:00 2001
Message-Id: <12a26b8b34df23103d4da6d7e40705485266a4d6.1714963068.git.mdw@distorted.org.uk>
From: Mark Wooding <mdw@chiark.greenend.org.uk>
Date: Mon, 27 Jun 2011 09:31:48 +0100
Subject: [PATCH] server/keyset.c: Return more informative error codes from
 ks_decrypt.
Organization: Straylight/Edgeware

From: Mark Wooding <mdw@distorted.org.uk>

Also, do what the commentary says and return zero and break the output
buffer if it's not big enough, rather than returning KSERR_DECRYPT.

The new error codes allow callers to make more sensible decisions about
whether to continue to search for other keys which might work better.
---
 server/keyexch.c |  1 +
 server/keyset.c  | 22 ++++++++++++----------
 server/tripe.h   |  2 ++
 3 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/server/keyexch.c b/server/keyexch.c
index d007a434..8eaf1e88 100644
--- a/server/keyexch.c
+++ b/server/keyexch.c
@@ -792,6 +792,7 @@ static int decryptrest(keyexch *kx, kxchal *kxc, unsigned msg, buf *b)
     a_warn("KX", "?PEER", kx->p, "decrypt-failed", "%s", pkname[msg], A_END);
     return (-1);
   }
+  if (!BOK(&bb)) return (-1);
   buf_init(b, BBASE(&bb), BLEN(&bb));
   return (0);
 }
diff --git a/server/keyset.c b/server/keyset.c
index 99fad2f5..1f580ff7 100644
--- a/server/keyset.c
+++ b/server/keyset.c
@@ -188,7 +188,7 @@ static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
 
   if (psz < ivsz + SEQSZ + tagsz) {
     T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
-    return (KSERR_DECRYPT);
+    return (KSERR_MALFORMED);
   }
   sz = psz - ivsz - SEQSZ - tagsz;
   pmac = BCUR(b); pseq = pmac + tagsz; piv = pseq + SEQSZ; ppk = piv + ivsz;
@@ -421,7 +421,7 @@ int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
  *		@buf *b@ = pointer to an input buffer
  *		@buf *bb@ = pointer to an output buffer
  *
- * Returns:	Zero on success; @KSERR_DECRYPT@ on failure.  Also returns
+ * Returns:	Zero on success; @KSERR_...@ on failure.  Also returns
  *		zero if there was insufficient buffer (but the output buffer
  *		is broken in this case).
  *
@@ -434,12 +434,12 @@ int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
 {
   time_t now = time(0);
   uint32 seq;
+  int err;
 
-  if (!KEYOK(ks, now) ||
-      buf_ensure(bb, BLEN(b)) ||
-      dodecrypt(ks, ty, b, bb, &seq) ||
-      seq_check(&ks->iseq, seq, "SYMM"))
-    return (KSERR_DECRYPT);
+  if (!KEYOK(ks, now)) return (KSERR_DECRYPT);
+  if (buf_ensure(bb, BLEN(b))) return (0);
+  if ((err = dodecrypt(ks, ty, b, bb, &seq)) != 0) return (err);
+  if (seq_check(&ks->iseq, seq, "SYMM")) return (KSERR_SEQ);
   return (0);
 }
 
@@ -574,24 +574,26 @@ int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
   time_t now = time(0);
   keyset *ks;
   uint32 seq;
+  int err;
 
   if (buf_ensure(bb, BLEN(b)))
-    return (KSERR_DECRYPT);
+    return (0);
 
   for (ks = *ksroot; ks; ks = ks->next) {
     if (!KEYOK(ks, now))
       continue;
-    if (!dodecrypt(ks, ty, b, bb, &seq)) {
+    if ((err = dodecrypt(ks, ty, b, bb, &seq)) == 0) {
       if (ks->f & KSF_LISTEN) {
 	T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
 		 ks->seq); )
 	ks->f &= ~KSF_LISTEN;
       }
       if (seq_check(&ks->iseq, seq, "SYMM"))
-	return (KSERR_DECRYPT);
+	return (KSERR_SEQ);
       else
 	return (0);
     }
+    if (err != KSERR_DECRYPT) return (err);
   }
   T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
   return (KSERR_DECRYPT);
diff --git a/server/tripe.h b/server/tripe.h
index c5694dc1..e382487b 100644
--- a/server/tripe.h
+++ b/server/tripe.h
@@ -226,6 +226,8 @@ typedef struct keyset {
 #define KSERR_REGEN -1			/* Regenerate keys */
 #define KSERR_NOKEYS -2			/* No keys left */
 #define KSERR_DECRYPT -3		/* Unable to decrypt message */
+#define KSERR_SEQ -4			/* Incorrect sequence number */
+#define KSERR_MALFORMED -5		/* Input ciphertext is broken */
 
 /* --- Key exchange --- *
  *
-- 
[mdw]