[PATCH 31/35] crypto: hash - Zap unaligned buffers

[Herbert Xu]

crypto: hash - Zap unaligned buffers

Some unaligned buffers on the stack weren't zapped properly which
may cause secret data to be leaked.  This patch fixes them by doing
a zero memset.

It is also possible for us to place random kernel stack contents
in the digest buffer if a digest operation fails.  This is fixed
by only copying if the operation succeeded.

Signed-off-by: Herbert Xu <herb...@gondor.apana.org.au>
---

 crypto/ahash.c |    3 +--
 crypto/shash.c |   14 +++++++++++---
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/crypto/ahash.c b/crypto/ahash.c
index cc824ef..1576f95 100644
--- a/crypto/ahash.c
+++ b/crypto/ahash.c
@@ -152,8 +152,7 @@ static int ahash_setkey_unaligned(struct crypto_ahash *tfm, 
const u8 *key,
        alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
        memcpy(alignbuffer, key, keylen);
        ret = ahash->setkey(tfm, alignbuffer, keylen);
-       memset(alignbuffer, 0, keylen);
-       kfree(buffer);
+       kzfree(buffer);
        return ret;
 }
 
diff --git a/crypto/shash.c b/crypto/shash.c
index fd92c03..e543283 100644
--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -45,8 +45,7 @@ static int shash_setkey_unaligned(struct crypto_shash *tfm, 
const u8 *key,
        alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
        memcpy(alignbuffer, key, keylen);
        err = shash->setkey(tfm, alignbuffer, keylen);
-       memset(alignbuffer, 0, keylen);
-       kfree(buffer);
+       kzfree(buffer);
        return err;
 }
 
@@ -79,13 +78,16 @@ static int shash_update_unaligned(struct shash_desc *desc, 
const u8 *data,
                                     ((unsigned long)data & alignmask);
        u8 buf[shash_align_buffer_size(unaligned_len, alignmask)]
                __attribute__ ((aligned));
+       int err;
 
        if (unaligned_len > len)
                unaligned_len = len;
 
        memcpy(buf, data, unaligned_len);
+       err = shash->update(desc, buf, unaligned_len);
+       memset(buf, 0, unaligned_len);
 
-       return shash->update(desc, buf, unaligned_len) ?:
+       return err ?:
               shash->update(desc, data + unaligned_len, len - unaligned_len);
 }
 
@@ -114,7 +116,13 @@ static int shash_final_unaligned(struct shash_desc *desc, 
u8 *out)
        int err;
 
        err = shash->final(desc, buf);
+       if (err)
+               goto out;
+
        memcpy(out, buf, ds);
+
+out:
+       memset(buf, 0, ds);
        return err;
 }
 
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