[PATCH RFC 1/6] crypto, dm: LLVMLinux: Remove VLAIS usage from dm-crypt

[behanw@converseincode.com]

From: Jan-Simon Möller <dl9pf@gmx.de>

The use of variable length arrays in structs (VLAIS) in the Linux Kernel code
precludes the use of compilers which don't implement VLAIS (for instance the
Clang compiler). This patch instead allocates the appropriate amount of memory
using an char array.

struct shash_desc contains a flexible array member member ctx declared with
CRYPTO_MINALIGN_ATTR, so sizeof(struct shash_desc) aligns the beginning
of the array declared after struct shash_desc with long long.

No trailing padding is required because it is not a struct type that can
be used in an array.

The CRYPTO_MINALIGN_ATTR is required so that desc is aligned with long long
as would be the case for a struct containing a member with
CRYPTO_MINALIGN_ATTR.

Signed-off-by: Jan-Simon Möller <dl9pf@gmx.de>
Signed-off-by: Behan Webster <behanw@converseincode.com>
Cc: pageexec@freemail.hu
---
 drivers/md/dm-crypt.c | 38 ++++++++++++++++++--------------------
 1 file changed, 18 insertions(+), 20 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index cd15e08..4d940d3 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -526,29 +526,28 @@ static int crypt_iv_lmk_one(struct crypt_config *cc, u8 *iv,
 			    u8 *data)
 {
 	struct iv_lmk_private *lmk = &cc->iv_gen_private.lmk;
-	struct {
-		struct shash_desc desc;
-		char ctx[crypto_shash_descsize(lmk->hash_tfm)];
-	} sdesc;
+	char sdesc[sizeof(struct shash_desc)
+		+ crypto_shash_descsize(lmk->hash_tfm)] CRYPTO_MINALIGN_ATTR;
+	struct shash_desc *desc = (struct shash_desc *)sdesc;
 	struct md5_state md5state;
 	__le32 buf[4];
 	int i, r;
 
-	sdesc.desc.tfm = lmk->hash_tfm;
-	sdesc.desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+	desc->tfm = lmk->hash_tfm;
+	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 
-	r = crypto_shash_init(&sdesc.desc);
+	r = crypto_shash_init(desc);
 	if (r)
 		return r;
 
 	if (lmk->seed) {
-		r = crypto_shash_update(&sdesc.desc, lmk->seed, LMK_SEED_SIZE);
+		r = crypto_shash_update(desc, lmk->seed, LMK_SEED_SIZE);
 		if (r)
 			return r;
 	}
 
 	/* Sector is always 512B, block size 16, add data of blocks 1-31 */
-	r = crypto_shash_update(&sdesc.desc, data + 16, 16 * 31);
+	r = crypto_shash_update(desc, data + 16, 16 * 31);
 	if (r)
 		return r;
 
@@ -557,12 +556,12 @@ static int crypt_iv_lmk_one(struct crypt_config *cc, u8 *iv,
 	buf[1] = cpu_to_le32((((u64)dmreq->iv_sector >> 32) & 0x00FFFFFF) | 0x80000000);
 	buf[2] = cpu_to_le32(4024);
 	buf[3] = 0;
-	r = crypto_shash_update(&sdesc.desc, (u8 *)buf, sizeof(buf));
+	r = crypto_shash_update(desc, (u8 *)buf, sizeof(buf));
 	if (r)
 		return r;
 
 	/* No MD5 padding here */
-	r = crypto_shash_export(&sdesc.desc, &md5state);
+	r = crypto_shash_export(desc, &md5state);
 	if (r)
 		return r;
 
@@ -679,10 +678,9 @@ static int crypt_iv_tcw_whitening(struct crypt_config *cc,
 	struct iv_tcw_private *tcw = &cc->iv_gen_private.tcw;
 	u64 sector = cpu_to_le64((u64)dmreq->iv_sector);
 	u8 buf[TCW_WHITENING_SIZE];
-	struct {
-		struct shash_desc desc;
-		char ctx[crypto_shash_descsize(tcw->crc32_tfm)];
-	} sdesc;
+	char sdesc[sizeof(struct shash_desc)
+		+ crypto_shash_descsize(tcw->crc32_tfm)] CRYPTO_MINALIGN_ATTR;
+	struct shash_desc *desc = (struct shash_desc *)sdesc;
 	int i, r;
 
 	/* xor whitening with sector number */
@@ -691,16 +689,16 @@ static int crypt_iv_tcw_whitening(struct crypt_config *cc,
 	crypto_xor(&buf[8], (u8 *)&sector, 8);
 
 	/* calculate crc32 for every 32bit part and xor it */
-	sdesc.desc.tfm = tcw->crc32_tfm;
-	sdesc.desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+	desc->tfm = tcw->crc32_tfm;
+	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 	for (i = 0; i < 4; i++) {
-		r = crypto_shash_init(&sdesc.desc);
+		r = crypto_shash_init(desc);
 		if (r)
 			goto out;
-		r = crypto_shash_update(&sdesc.desc, &buf[i * 4], 4);
+		r = crypto_shash_update(desc, &buf[i * 4], 4);
 		if (r)
 			goto out;
-		r = crypto_shash_final(&sdesc.desc, &buf[i * 4]);
+		r = crypto_shash_final(desc, &buf[i * 4]);
 		if (r)
 			goto out;
 	}
-- 
1.9.1

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