Patch "fscrypto: make XTS tweak initialization endian-independent" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

fscrypto: make XTS tweak initialization endian-independent

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fscrypto-make-xts-tweak-initialization-endian-independent.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Biggers <[email protected]>
Date: Wed, 12 Oct 2016 23:30:16 -0400
Subject: fscrypto: make XTS tweak initialization endian-independent

From: Eric Biggers <[email protected]>

commit fb4454376df9d820d95452d71dd83da6971f9338 upstream.

The XTS tweak (or IV) was initialized differently on little endian and big endian systems. Because the ciphertext depends on the XTS tweak, it was not possible to use an encrypted filesystem created by a little endian system on a big endian system and vice versa, even if they shared the same PAGE_SIZE. Fix this by always using little endian.

This will break hypothetical big endian users of ext4 or f2fs encryption. However, all users we are aware of are little endian, and it's believed that "real" big endian users are unlikely to exist yet. So this might as well be fixed now before it's too late.

---
 fs/crypto/crypto.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

@@ -152,7 +152,10 @@ static int do_page_crypto(struct inode *
 			struct page *src_page, struct page *dest_page,
 			gfp_t gfp_flags)
 {
-	u8 xts_tweak[FS_XTS_TWEAK_SIZE];
+	struct {
+		__le64 index;
+		u8 padding[FS_XTS_TWEAK_SIZE - sizeof(__le64)];
+	} xts_tweak;
 	struct skcipher_request *req = NULL;
 	DECLARE_FS_COMPLETION_RESULT(ecr);
 	struct scatterlist dst, src;

@@ -172,17 +175,15 @@ static int do_page_crypto(struct inode *
 		req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 		fscrypt_complete, &ecr);
 
-	BUILD_BUG_ON(FS_XTS_TWEAK_SIZE < sizeof(index));
-	memcpy(xts_tweak, &index, sizeof(index));
-	memset(&xts_tweak[sizeof(index)], 0,
-			FS_XTS_TWEAK_SIZE - sizeof(index));
+	BUILD_BUG_ON(sizeof(xts_tweak) != FS_XTS_TWEAK_SIZE);
+	xts_tweak.index = cpu_to_le64(index);
+	memset(xts_tweak.padding, 0, sizeof(xts_tweak.padding));
 
 	sg_init_table(&dst, 1);
 	sg_set_page(&dst, dest_page, PAGE_SIZE, 0);
 	sg_init_table(&src, 1);
 	sg_set_page(&src, src_page, PAGE_SIZE, 0);
-	skcipher_request_set_crypt(req, &src, &dst, PAGE_SIZE,
-					xts_tweak);
+	skcipher_request_set_crypt(req, &src, &dst, PAGE_SIZE, &xts_tweak);
 	if (rw == FS_DECRYPT)
 		res = crypto_skcipher_decrypt(req);
 	else

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/fscrypto-lock-inode-while-setting-encryption-policy.patch queue-4.8/ext4-do-not-advertise-encryption-support-when-disabled.patch queue-4.8/fscrypto-make-xts-tweak-initialization-endian-independent.patch