[hurd] 11/25: random: Hash continuous areas in the csprng pool.

[Samuel Thibault]

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sthibault pushed a commit to branch upstream
in repository hurd.

commit 4fb81a7e92d0cd6d854a4a020f34b948ad6ce29b
Author: Justus Winter <address@hidden>
Date:   Tue Sep 6 09:47:02 2016 +0200

    random: Hash continuous areas in the csprng pool.
    
    * random/gnupg-random.c (mix_pool): Store the first hash at the end of
    the pool.
    
    --
    
    This fixes a long standing bug (since 1998) in Libgcrypt and GnuPG.
    An attacker who obtains 580 bytes of the random number from the
    standard RNG can trivially predict the next 20 bytes of output.
    
    The bug was found and reported by Felix Dörre and Vladimir Klebanov,
    Karlsruhe Institute of Technology.  A paper describing the problem in
    detail will shortly be published.
    
    This is a port of c6dbfe89 from the GnuPG classic branch.
    
    CVE-id: CVE-2016-6313
---
 random/gnupg-random.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/random/gnupg-random.c b/random/gnupg-random.c
index 3cf7812..a4df694 100644
--- a/random/gnupg-random.c
+++ b/random/gnupg-random.c
@@ -276,23 +276,21 @@ mix_pool(byte *pool)
  #if DIGESTLEN != 20
     #error must have a digest length of 20 for ripe-md-160
  #endif
-    /* loop over the pool */
+    /* pool -> pool' */
     pend = pool + POOLSIZE;
     memcpy(hashbuf, pend - DIGESTLEN, DIGESTLEN );
     memcpy(hashbuf+DIGESTLEN, pool, BLOCKLEN-DIGESTLEN);
     rmd160_mixblock( &md, hashbuf);
-    memcpy(pool, hashbuf, 20 );
+    memcpy(pool, hashbuf, DIGESTLEN);
 
+    /* Loop for the remaining iterations.  */
     p = pool;
     for( n=1; n < POOLBLOCKS; n++ ) {
-       memcpy(hashbuf, p, DIGESTLEN );
-
-       p += DIGESTLEN;
-       if( p+DIGESTLEN+BLOCKLEN < pend )
-           memcpy(hashbuf+DIGESTLEN, p+DIGESTLEN, BLOCKLEN-DIGESTLEN);
+       if( p + BLOCKLEN < pend )
+           memcpy(hashbuf, p, BLOCKLEN);
        else {
-           byte *pp = p+DIGESTLEN;
-           for(i=DIGESTLEN; i < BLOCKLEN; i++ ) {
+           byte *pp = p;
+           for(i=0; i < BLOCKLEN; i++ ) {
                if( pp >= pend )
                    pp = pool;
                hashbuf[i] = *pp++;
@@ -300,7 +298,8 @@ mix_pool(byte *pool)
        }
 
        rmd160_mixblock( &md, hashbuf);
-       memcpy(p, hashbuf, 20 );
+       p += DIGESTLEN;
+       memcpy(p, hashbuf, DIGESTLEN);
     }
     burn_stack (200); /* for the rmd160_mixblock() */
 }

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