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From 603a58f73e71323294c0d840bbfef4b5d9676e32 Mon Sep 17 00:00:00 2001
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Message-Id: <603a58f73e71323294c0d840bbfef4b5d9676e32@dist-git>
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From: "Daniel P. Berrange" <berrange@redhat.com>
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Date: Wed, 3 May 2017 08:52:13 +0200
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Subject: [PATCH] Fix padding of encrypted data
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If we are encoding a block of data that is 16 bytes in length,
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we cannot leave it as 16 bytes, we must pad it out to the next
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block boundary, 32 bytes. Without this padding, the decoder will
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incorrectly treat the last byte of plain text as the padding
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length, as it can't distinguish padded from non-padded data.
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The problem exhibited itself when using a 16 byte passphrase
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for a LUKS volume
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$ virsh secret-set-value 55806c7d-8e93-456f-829b-607d8c198367 \
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$(echo -n 1234567812345678 | base64)
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Secret value set
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$ virsh start demo
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error: Failed to start domain demo
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error: internal error: process exited while connecting to monitor: >>>>>>>>>>Len 16
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2017-05-02T10:35:40.016390Z qemu-system-x86_64: -object \
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secret,id=virtio-disk1-luks-secret0,data=SEtNi5vDUeyseMKHwc1c1Q==,\
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keyid=masterKey0,iv=zm7apUB1A6dPcH53VW960Q==,format=base64: \
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Incorrect number of padding bytes (56) found on decrypted data
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Notice how the padding '56' corresponds to the ordinal value of
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the character '8'.
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Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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(cherry picked from commit 71890992daf37ec78b00b4ce873369421dc99731)
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https://bugzilla.redhat.com/show_bug.cgi?id=1447297
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Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
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---
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src/util/vircrypto.c | 10 ++++++++--
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1 file changed, 8 insertions(+), 2 deletions(-)
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diff --git a/src/util/vircrypto.c b/src/util/vircrypto.c
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index 8748e1c4e..48b04fc8c 100644
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--- a/src/util/vircrypto.c
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+++ b/src/util/vircrypto.c
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@@ -152,8 +152,14 @@ virCryptoEncryptDataAESgnutls(gnutls_cipher_algorithm_t gnutls_enc_alg,
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uint8_t *ciphertext;
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size_t ciphertextlen;
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- /* Allocate a padded buffer, copy in the data */
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- ciphertextlen = VIR_ROUND_UP(datalen, 16);
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+ /* Allocate a padded buffer, copy in the data.
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+ *
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+ * NB, we must *always* have at least 1 byte of
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+ * padding - we can't skip it on multiples of
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+ * 16, otherwise decoder can't distinguish padded
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+ * data from non-padded data. Hence datalen + 1
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+ */
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+ ciphertextlen = VIR_ROUND_UP(datalen + 1, 16);
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if (VIR_ALLOC_N(ciphertext, ciphertextlen) < 0)
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return -1;
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memcpy(ciphertext, data, datalen);
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--
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2.12.2
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