crypto: lrw - Fix out-of bounds access on counter overflow

commit fbe1a850b3b1522e9fc22319ccbbcd2ab05328d2 upstream.

When the LRW block counter overflows, the current implementation returns
128 as the index to the precomputed multiplication table, which has 128
entries. This patch fixes it to return the correct value (127).

Fixes: 64470f1b8510 ("[CRYPTO] lrw: Liskov Rivest Wagner, a tweakable narrow block cipher mode")
Cc: <stable@vger.kernel.org> # 2.6.20+
Reported-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/crypto/lrw.c b/crypto/lrw.c
index 6f9908a7ebcbe19f76a4ee306f326f291aff8de9..d38a382b09eb6c28670a3644c0f4706ce8dccdac 100644 (file)
--- a/crypto/lrw.c
+++ b/crypto/lrw.c
@@ -132,7 +132,12 @@ static inline int get_index128(be128 *block)
                return x + ffz(val);
        }
 
-       return x;
+       /*
+        * If we get here, then x == 128 and we are incrementing the counter
+        * from all ones to all zeros. This means we must return index 127, i.e.
+        * the one corresponding to key2*{ 1,...,1 }.
+        */
+       return 127;
 }
 
 static int crypt(struct blkcipher_desc *d,