[PATCH 4/7] ecryptfs: use sg_init_one() instead of virt_to_scatterlist()

[Tal Zussman]

Every caller passes a kmalloc()-ed buffer or an array inside a kmalloc()-ed
structure, which is physically contiguous and so fits in one
scatterlist entry. Use sg_init_one(), which can't fail, drop the
two-entry arrays and their length checks, and remove
virt_to_scatterlist() and the unused ECRYPTFS_MAX_SCATTERLIST_LEN.

Signed-off-by: Tal Zussman <tz2294@xxxxxxxxxxxx>
---
 fs/ecryptfs/crypto.c          |  46 -----------------
 fs/ecryptfs/ecryptfs_kernel.h |   2 -
 fs/ecryptfs/keystore.c        | 114 +++++++++---------------------------------
 3 files changed, 25 insertions(+), 137 deletions(-)

diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index 6a014872e919..f0e67b48917f 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -149,50 +149,6 @@ void ecryptfs_destroy_mount_crypt_stat(
 	memset(mount_crypt_stat, 0, sizeof(struct ecryptfs_mount_crypt_stat));
 }
 
-/**
- * virt_to_scatterlist
- * @addr: Virtual address
- * @size: Size of data; should be an even multiple of the block size
- * @sg: Pointer to scatterlist array; set to NULL to obtain only
- *      the number of scatterlist structs required in array
- * @sg_size: Max array size
- *
- * Fills in a scatterlist array with page references for a passed
- * virtual address.
- *
- * Returns the number of scatterlist structs in array used
- */
-int virt_to_scatterlist(const void *addr, int size, struct scatterlist *sg,
-			int sg_size)
-{
-	int i = 0;
-	struct page *pg;
-	int offset;
-	int remainder_of_page;
-
-	sg_init_table(sg, sg_size);
-
-	while (size > 0 && i < sg_size) {
-		pg = virt_to_page(addr);
-		offset = offset_in_page(addr);
-		sg_set_page(&sg[i], pg, 0, offset);
-		remainder_of_page = PAGE_SIZE - offset;
-		if (size >= remainder_of_page) {
-			sg[i].length = remainder_of_page;
-			addr += remainder_of_page;
-			size -= remainder_of_page;
-		} else {
-			sg[i].length = size;
-			addr += size;
-			size = 0;
-		}
-		i++;
-	}
-	if (size > 0)
-		return -ENOMEM;
-	return i;
-}
-
 /**
  * crypt_scatterlist
  * @crypt_stat: Pointer to the crypt_stat struct to initialize.
@@ -438,8 +394,6 @@ int ecryptfs_decrypt_page(struct folio *folio)
 	return rc;
 }
 
-#define ECRYPTFS_MAX_SCATTERLIST_LEN 4
-
 /**
  * ecryptfs_init_crypt_ctx
  * @crypt_stat: Uninitialized crypt stats structure
diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index ff5cef83c79c..6a74a2bfc833 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -541,8 +541,6 @@ int ecryptfs_encrypt_and_encode_filename(
 	struct ecryptfs_mount_crypt_stat *mount_crypt_stat,
 	const char *name, size_t name_size);
 void ecryptfs_dump_hex(char *data, int bytes);
-int virt_to_scatterlist(const void *addr, int size, struct scatterlist *sg,
-			int sg_size);
 int ecryptfs_compute_root_iv(struct ecryptfs_crypt_stat *crypt_stat);
 void ecryptfs_rotate_iv(unsigned char *iv);
 void ecryptfs_init_crypt_stat(struct ecryptfs_crypt_stat *crypt_stat);
diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index 51651314b7a6..051f7948cf52 100644
--- a/fs/ecryptfs/keystore.c
+++ b/fs/ecryptfs/keystore.c
@@ -595,8 +595,8 @@ struct ecryptfs_write_tag_70_packet_silly_stack {
 	struct mutex *tfm_mutex;
 	char *block_aligned_filename;
 	struct ecryptfs_auth_tok *auth_tok;
-	struct scatterlist src_sg[2];
-	struct scatterlist dst_sg[2];
+	struct scatterlist src_sg;
+	struct scatterlist dst_sg;
 	struct crypto_skcipher *skcipher_tfm;
 	struct skcipher_request *skcipher_req;
 	char iv[ECRYPTFS_MAX_IV_BYTES];
@@ -751,24 +751,9 @@ ecryptfs_write_tag_70_packet(char *dest, size_t *remaining_bytes,
 	}
 	memcpy(&s->block_aligned_filename[s->num_rand_bytes], filename,
 	       filename_size);
-	rc = virt_to_scatterlist(s->block_aligned_filename,
-				 s->block_aligned_filename_size, s->src_sg, 2);
-	if (rc < 1) {
-		printk(KERN_ERR "%s: Internal error whilst attempting to "
-		       "convert filename memory to scatterlist; rc = [%d]. "
-		       "block_aligned_filename_size = [%zd]\n", __func__, rc,
-		       s->block_aligned_filename_size);
-		goto out_free_unlock;
-	}
-	rc = virt_to_scatterlist(&dest[s->i], s->block_aligned_filename_size,
-				 s->dst_sg, 2);
-	if (rc < 1) {
-		printk(KERN_ERR "%s: Internal error whilst attempting to "
-		       "convert encrypted filename memory to scatterlist; "
-		       "rc = [%d]. block_aligned_filename_size = [%zd]\n",
-		       __func__, rc, s->block_aligned_filename_size);
-		goto out_free_unlock;
-	}
+	sg_init_one(&s->src_sg, s->block_aligned_filename,
+		    s->block_aligned_filename_size);
+	sg_init_one(&s->dst_sg, &dest[s->i], s->block_aligned_filename_size);
 	/* The characters in the first block effectively do the job
 	 * of the IV here, so we just use 0's for the IV. Note the
 	 * constraint that ECRYPTFS_FILENAME_MIN_RANDOM_PREPEND_BYTES
@@ -787,7 +772,7 @@ ecryptfs_write_tag_70_packet(char *dest, size_t *remaining_bytes,
 		       mount_crypt_stat->global_default_fn_cipher_key_bytes);
 		goto out_free_unlock;
 	}
-	skcipher_request_set_crypt(s->skcipher_req, s->src_sg, s->dst_sg,
+	skcipher_request_set_crypt(s->skcipher_req, &s->src_sg, &s->dst_sg,
 				   s->block_aligned_filename_size, s->iv);
 	rc = crypto_skcipher_encrypt(s->skcipher_req);
 	if (rc) {
@@ -823,8 +808,8 @@ struct ecryptfs_parse_tag_70_packet_silly_stack {
 	struct mutex *tfm_mutex;
 	char *decrypted_filename;
 	struct ecryptfs_auth_tok *auth_tok;
-	struct scatterlist src_sg[2];
-	struct scatterlist dst_sg[2];
+	struct scatterlist src_sg;
+	struct scatterlist dst_sg;
 	struct crypto_skcipher *skcipher_tfm;
 	struct skcipher_request *skcipher_req;
 	char fnek_sig_hex[ECRYPTFS_SIG_SIZE_HEX + 1];
@@ -943,15 +928,8 @@ ecryptfs_parse_tag_70_packet(char **filename, size_t *filename_size,
 		goto out;
 	}
 	mutex_lock(s->tfm_mutex);
-	rc = virt_to_scatterlist(&data[(*packet_size)],
-				 s->block_aligned_filename_size, s->src_sg, 2);
-	if (rc < 1) {
-		printk(KERN_ERR "%s: Internal error whilst attempting to "
-		       "convert encrypted filename memory to scatterlist; "
-		       "rc = [%d]. block_aligned_filename_size = [%zd]\n",
-		       __func__, rc, s->block_aligned_filename_size);
-		goto out_unlock;
-	}
+	sg_init_one(&s->src_sg, &data[(*packet_size)],
+		    s->block_aligned_filename_size);
 	(*packet_size) += s->block_aligned_filename_size;
 	s->decrypted_filename = kmalloc(s->block_aligned_filename_size,
 					GFP_KERNEL);
@@ -959,15 +937,8 @@ ecryptfs_parse_tag_70_packet(char **filename, size_t *filename_size,
 		rc = -ENOMEM;
 		goto out_unlock;
 	}
-	rc = virt_to_scatterlist(s->decrypted_filename,
-				 s->block_aligned_filename_size, s->dst_sg, 2);
-	if (rc < 1) {
-		printk(KERN_ERR "%s: Internal error whilst attempting to "
-		       "convert decrypted filename memory to scatterlist; "
-		       "rc = [%d]. block_aligned_filename_size = [%zd]\n",
-		       __func__, rc, s->block_aligned_filename_size);
-		goto out_free_unlock;
-	}
+	sg_init_one(&s->dst_sg, s->decrypted_filename,
+		    s->block_aligned_filename_size);
 
 	s->skcipher_req = skcipher_request_alloc(s->skcipher_tfm, GFP_KERNEL);
 	if (!s->skcipher_req) {
@@ -1007,7 +978,7 @@ ecryptfs_parse_tag_70_packet(char **filename, size_t *filename_size,
 		       mount_crypt_stat->global_default_fn_cipher_key_bytes);
 		goto out_free_unlock;
 	}
-	skcipher_request_set_crypt(s->skcipher_req, s->src_sg, s->dst_sg,
+	skcipher_request_set_crypt(s->skcipher_req, &s->src_sg, &s->dst_sg,
 				   s->block_aligned_filename_size, s->iv);
 	rc = crypto_skcipher_decrypt(s->skcipher_req);
 	if (rc) {
@@ -1625,8 +1596,8 @@ static int
 decrypt_passphrase_encrypted_session_key(struct ecryptfs_auth_tok *auth_tok,
 					 struct ecryptfs_crypt_stat *crypt_stat)
 {
-	struct scatterlist dst_sg[2];
-	struct scatterlist src_sg[2];
+	struct scatterlist dst_sg;
+	struct scatterlist src_sg;
 	struct mutex *tfm_mutex;
 	struct crypto_skcipher *tfm;
 	struct skcipher_request *req = NULL;
@@ -1648,28 +1619,12 @@ decrypt_passphrase_encrypted_session_key(struct ecryptfs_auth_tok *auth_tok,
 		       crypt_stat->cipher, rc);
 		goto out;
 	}
-	rc = virt_to_scatterlist(auth_tok->session_key.encrypted_key,
-				 auth_tok->session_key.encrypted_key_size,
-				 src_sg, 2);
-	if (rc < 1 || rc > 2) {
-		printk(KERN_ERR "Internal error whilst attempting to convert "
-			"auth_tok->session_key.encrypted_key to scatterlist; "
-			"expected rc = 1; got rc = [%d]. "
-		       "auth_tok->session_key.encrypted_key_size = [%d]\n", rc,
-			auth_tok->session_key.encrypted_key_size);
-		goto out;
-	}
+	sg_init_one(&src_sg, auth_tok->session_key.encrypted_key,
+		    auth_tok->session_key.encrypted_key_size);
 	auth_tok->session_key.decrypted_key_size =
 		auth_tok->session_key.encrypted_key_size;
-	rc = virt_to_scatterlist(auth_tok->session_key.decrypted_key,
-				 auth_tok->session_key.decrypted_key_size,
-				 dst_sg, 2);
-	if (rc < 1 || rc > 2) {
-		printk(KERN_ERR "Internal error whilst attempting to convert "
-			"auth_tok->session_key.decrypted_key to scatterlist; "
-			"expected rc = 1; got rc = [%d]\n", rc);
-		goto out;
-	}
+	sg_init_one(&dst_sg, auth_tok->session_key.decrypted_key,
+		    auth_tok->session_key.decrypted_key_size);
 	mutex_lock(tfm_mutex);
 	req = skcipher_request_alloc(tfm, GFP_KERNEL);
 	if (!req) {
@@ -1692,7 +1647,7 @@ decrypt_passphrase_encrypted_session_key(struct ecryptfs_auth_tok *auth_tok,
 		rc = -EINVAL;
 		goto out;
 	}
-	skcipher_request_set_crypt(req, src_sg, dst_sg,
+	skcipher_request_set_crypt(req, &src_sg, &dst_sg,
 				   auth_tok->session_key.encrypted_key_size,
 				   NULL);
 	rc = crypto_skcipher_decrypt(req);
@@ -2166,8 +2121,8 @@ write_tag_3_packet(char *dest, size_t *remaining_bytes,
 	size_t i;
 	size_t encrypted_session_key_valid = 0;
 	char session_key_encryption_key[ECRYPTFS_MAX_KEY_BYTES];
-	struct scatterlist dst_sg[2];
-	struct scatterlist src_sg[2];
+	struct scatterlist dst_sg;
+	struct scatterlist src_sg;
 	struct mutex *tfm_mutex = NULL;
 	u8 cipher_code;
 	size_t packet_size_length;
@@ -2242,27 +2197,8 @@ write_tag_3_packet(char *dest, size_t *remaining_bytes,
 		ecryptfs_printk(KERN_DEBUG, "Session key encryption key:\n");
 		ecryptfs_dump_hex(session_key_encryption_key, 16);
 	}
-	rc = virt_to_scatterlist(crypt_stat->key, key_rec->enc_key_size,
-				 src_sg, 2);
-	if (rc < 1 || rc > 2) {
-		ecryptfs_printk(KERN_ERR, "Error generating scatterlist "
-				"for crypt_stat session key; expected rc = 1; "
-				"got rc = [%d]. key_rec->enc_key_size = [%zd]\n",
-				rc, key_rec->enc_key_size);
-		rc = -ENOMEM;
-		goto out;
-	}
-	rc = virt_to_scatterlist(key_rec->enc_key, key_rec->enc_key_size,
-				 dst_sg, 2);
-	if (rc < 1 || rc > 2) {
-		ecryptfs_printk(KERN_ERR, "Error generating scatterlist "
-				"for crypt_stat encrypted session key; "
-				"expected rc = 1; got rc = [%d]. "
-				"key_rec->enc_key_size = [%zd]\n", rc,
-				key_rec->enc_key_size);
-		rc = -ENOMEM;
-		goto out;
-	}
+	sg_init_one(&src_sg, crypt_stat->key, key_rec->enc_key_size);
+	sg_init_one(&dst_sg, key_rec->enc_key, key_rec->enc_key_size);
 	mutex_lock(tfm_mutex);
 	rc = crypto_skcipher_setkey(tfm, session_key_encryption_key,
 				    crypt_stat->key_size);
@@ -2289,7 +2225,7 @@ write_tag_3_packet(char *dest, size_t *remaining_bytes,
 	rc = 0;
 	ecryptfs_printk(KERN_DEBUG, "Encrypting [%zd] bytes of the key\n",
 			crypt_stat->key_size);
-	skcipher_request_set_crypt(req, src_sg, dst_sg,
+	skcipher_request_set_crypt(req, &src_sg, &dst_sg,
 				   (*key_rec).enc_key_size, NULL);
 	rc = crypto_skcipher_encrypt(req);
 	mutex_unlock(tfm_mutex);

-- 
2.39.5