f2fs crypto: add rwsem to avoid data races

Previoulsy, fi->i_crypt_info was not covered by any lock, resulting in memory leak.

This patch adds a rwsem to avoid leaking objects on i_crypt_info.

Signed-off-by Jaegeuk Kim <[email protected]>

Quoted 6 lines · Jaegeuk Kim

Previoulsy, fi->i_crypt_info was not covered by any lock, resulting in memory leak.

This patch adds a rwsem to avoid leaking objects on i_crypt_info.

Signed-off-by Jaegeuk Kim <[email protected]>

I'm not sure we need an rwsem to fix this issue. In terms of serializing the creation and deletion of the structure, it should be possible to use an cmpxchg() on the pointer itself. (e.g., if we lose the race on the creation side, we just release our structure and use the one that the winner allocated).

If we do end up needing to serialize access to the tfm in the i_crypt_info object for datapath reads/writes, then we might need a mutex, but I think that should be it, no?

- Ted

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Quoted 14 lines · Theodore Ts'o

Quoted 6 lines · Jaegeuk Kim

Previoulsy, fi->i_crypt_info was not covered by any lock, resulting in memory leak.

This patch adds a rwsem to avoid leaking objects on i_crypt_info.

Signed-off-by Jaegeuk Kim <[email protected]>

I'm not sure we need an rwsem to fix this issue. In terms of serializing the creation and deletion of the structure, it should be possible to use an cmpxchg() on the pointer itself. (e.g., if we lose the race on the creation side, we just release our structure and use the one that the winner allocated).

Quoted 6 lines

If we do end up needing to serialize access to the tfm in the i_crypt_info object for datapath reads/writes, then we might need a mutex, but I think that should be it, no?

- Ted

I have to agree with Ted here, as mutual exclusion locking is ideal for the scenario here of a reader vs writer exclusion. My only concern

is that can there be many readers to one writer here as if so reader/writer spin locks may be better.

Nick

Quoted 5 lines · nick

Quoted 2 lines · Theodore Ts'o

Quoted 1 line · Jaegeuk Kim

Previoulsy, fi->i_crypt_info was not covered by any lock,

resulting in

Quoted 8 lines

Quoted 8 lines

Quoted 5 lines

memory leak.

This patch adds a rwsem to avoid leaking objects on i_crypt_info.

Signed-off-by Jaegeuk Kim <[email protected]>

I'm not sure we need an rwsem to fix this issue. In terms of serializing the creation and deletion of the structure, it should

be

Quoted 1 line

Quoted 1 line

possible to use an cmpxchg() on the pointer itself. (e.g., if we

lose

Quoted 1 line

Quoted 1 line

the race on the creation side, we just release our structure and

use

Quoted 10 lines

Quoted 8 lines

the one that the winner allocated).

If we do end up needing to serialize access to the tfm in the i_crypt_info object for datapath reads/writes, then we might need a mutex, but I think that should be it, no?

- Ted

I have to agree with Ted here, as mutual exclusion locking is ideal for the scenario here of a reader vs writer exclusion. My only

concern

What I'm saying is writer vs writer actually.

Quoted 1 line

is that can there be many readers to one writer here as if so

reader/writer

Quoted 1 line

spin locks may be better.

I could write another patch using a rwlock by removing needless down_write for
f2fs_free_encryption_info.

Thanks,

Quoted 1 line

Nick

What I'm saying is writer vs writer actually.

From 6a57d7bbf7bd2d31432e55f266543bb56bf7e1fc Mon Sep 17 00:00:00 2001

Quoted 2 lines · Jaegeuk Kim

What I'm saying is writer vs writer actually.

This is a rough draft of what I had in mind. This fixes the tfm allocation issue in the writepage path, as well as using a lockless cmpxchg algorithm to address the race you were concerned about.

What do you think? I'm still running xfstests, and I want to do another desk check of the code tomorrow after I get a good night's sleep, but it does pass my quick smoketest script, and enough of xfstests's quick test group that any bugs left are probably the more subtle ones.

- Ted

Quoted 1 line

From 6a57d7bbf7bd2d31432e55f266543bb56bf7e1fc Mon Sep 17 00:00:00 2001

From: Theodore Ts'o <[email protected]>
Date: Wed, 20 May 2015 00:27:45 -0400
Subject: [PATCH] ext4 crypto: use per-inode tfm structure

As suggested by Herbert Xu, we shouldn't allocate a new tfm each time we read or write a page. Instead we can use a single tfm hanging off the inode's crypt_info structure for all of our encryption needs for that inode, since the tfm can be used by multiple crypto requests in parallel.

Also use cmpxchg() to avoid races that could result in crypt_info structure getting doubly allocated or doubly freed.

Signed-off-by Theodore Ts'o <[email protected]>

---
 fs/ext4/crypto.c       |  61 ++--------------------------
 fs/ext4/crypto_fname.c |  48 +---------------------
 fs/ext4/crypto_key.c   | 108 +++++++++++++++++++++++++++++++++++--------------
 fs/ext4/dir.c          |   3 --
 fs/ext4/ext4.h         |   5 +--
 fs/ext4/ext4_crypto.h  |   3 --
 fs/ext4/namei.c        |  17 ++++----
 fs/ext4/super.c        |   2 +-
 fs/ext4/symlink.c      |   2 +-
 9 files changed, 95 insertions(+), 154 deletions(-)

fs/ext4/crypto.c +3 -58

index 1484b58..68c7ab8 100644
@@ -80,8 +80,6 @@ void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
 	}
 	ctx->w.control_page = NULL;
 	if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
-		if (ctx->tfm)
-			crypto_free_tfm(ctx->tfm);
 		kmem_cache_free(ext4_crypto_ctx_cachep, ctx);
 	} else {
 		spin_lock_irqsave(&ext4_crypto_ctx_lock, flags);

@@ -136,36 +134,6 @@ struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
 	}
 	ctx->flags &= ~EXT4_WRITE_PATH_FL;
 
-	/* Allocate a new Crypto API context if we don't already have
-	 * one or if it isn't the right mode. */
-	if (ctx->tfm && (ctx->mode != ci->ci_data_mode)) {
-		crypto_free_tfm(ctx->tfm);
-		ctx->tfm = NULL;
-		ctx->mode = EXT4_ENCRYPTION_MODE_INVALID;
-	}
-	if (!ctx->tfm) {
-		switch (ci->ci_data_mode) {
-		case EXT4_ENCRYPTION_MODE_AES_256_XTS:
-			ctx->tfm = crypto_ablkcipher_tfm(
-				crypto_alloc_ablkcipher("xts(aes)", 0, 0));
-			break;
-		case EXT4_ENCRYPTION_MODE_AES_256_GCM:
-			/* TODO(mhalcrow): AEAD w/ gcm(aes);
-			 * crypto_aead_setauthsize() */
-			ctx->tfm = ERR_PTR(-ENOTSUPP);
-			break;
-		default:
-			BUG();
-		}
-		if (IS_ERR_OR_NULL(ctx->tfm)) {
-			res = PTR_ERR(ctx->tfm);
-			ctx->tfm = NULL;
-			goto out;
-		}
-		ctx->mode = ci->ci_data_mode;
-	}
-	BUG_ON(ci->ci_size != ext4_encryption_key_size(ci->ci_data_mode));
-
 out:
 	if (res) {
 		if (!IS_ERR_OR_NULL(ctx))

@@ -195,8 +163,6 @@ void ext4_exit_crypto(void)
 					     ext4_bounce_page_pool);
 			}
 		}
-		if (pos->tfm)
-			crypto_free_tfm(pos->tfm);
 		kmem_cache_free(ext4_crypto_ctx_cachep, pos);
 	}
 	INIT_LIST_HEAD(&ext4_free_crypto_ctxs);

@@ -312,32 +278,11 @@ static int ext4_page_crypto(struct ext4_crypto_ctx *ctx,
 	struct ablkcipher_request *req = NULL;
 	DECLARE_EXT4_COMPLETION_RESULT(ecr);
 	struct scatterlist dst, src;
-	struct ext4_inode_info *ei = EXT4_I(inode);
-	struct crypto_ablkcipher *atfm = __crypto_ablkcipher_cast(ctx->tfm);
+	struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
+	struct crypto_ablkcipher *tfm = ci->ci_ctfm;
 	int res = 0;
 
-	BUG_ON(!ctx->tfm);
-	BUG_ON(ctx->mode != ei->i_crypt_info->ci_data_mode);
-
-	if (ctx->mode != EXT4_ENCRYPTION_MODE_AES_256_XTS) {
-		printk_ratelimited(KERN_ERR
-				   "%s: unsupported crypto algorithm: %d\n",
-				   __func__, ctx->mode);
-		return -ENOTSUPP;
-	}
-
-	crypto_ablkcipher_clear_flags(atfm, ~0);
-	crypto_tfm_set_flags(ctx->tfm, CRYPTO_TFM_REQ_WEAK_KEY);
-
-	res = crypto_ablkcipher_setkey(atfm, ei->i_crypt_info->ci_raw,
-				       ei->i_crypt_info->ci_size);
-	if (res) {
-		printk_ratelimited(KERN_ERR
-				   "%s: crypto_ablkcipher_setkey() failed\n",
-				   __func__);
-		return res;
-	}
-	req = ablkcipher_request_alloc(atfm, GFP_NOFS);
+	req = ablkcipher_request_alloc(tfm, GFP_NOFS);
 	if (!req) {
 		printk_ratelimited(KERN_ERR
 				   "%s: crypto_request_alloc() failed\n",

fs/ext4/crypto_fname.c +1 -47

index e63dd29..29a2dc9 100644
@@ -252,52 +252,6 @@ static int digest_decode(const char *src, int len, char *dst)
 	return cp - dst;
 }
 
-int ext4_setup_fname_crypto(struct inode *inode)
-{
-	struct ext4_inode_info *ei = EXT4_I(inode);
-	struct ext4_crypt_info *ci = ei->i_crypt_info;
-	struct crypto_ablkcipher *ctfm;
-	int res;
-
-	/* Check if the crypto policy is set on the inode */
-	res = ext4_encrypted_inode(inode);
-	if (res == 0)
-		return 0;
-
-	res = ext4_get_encryption_info(inode);
-	if (res < 0)
-		return res;
-	ci = ei->i_crypt_info;
-
-	if (!ci || ci->ci_ctfm)
-		return 0;
-
-	if (ci->ci_filename_mode != EXT4_ENCRYPTION_MODE_AES_256_CTS) {
-		printk_once(KERN_WARNING "ext4: unsupported key mode %d\n",
-			    ci->ci_filename_mode);
-		return -ENOKEY;
-	}
-
-	ctfm = crypto_alloc_ablkcipher("cts(cbc(aes))", 0, 0);
-	if (!ctfm || IS_ERR(ctfm)) {
-		res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
-		printk(KERN_DEBUG "%s: error (%d) allocating crypto tfm\n",
-		       __func__, res);
-		return res;
-	}
-	crypto_ablkcipher_clear_flags(ctfm, ~0);
-	crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm),
-			     CRYPTO_TFM_REQ_WEAK_KEY);
-
-	res = crypto_ablkcipher_setkey(ctfm, ci->ci_raw, ci->ci_size);
-	if (res) {
-		crypto_free_ablkcipher(ctfm);
-		return -EIO;
-	}
-	ci->ci_ctfm = ctfm;
-	return 0;
-}
-
 /**
  * ext4_fname_crypto_round_up() -
  *

@@ -449,7 +403,7 @@ int ext4_fname_setup_filename(struct inode *dir, const struct qstr *iname,
 		fname->disk_name.len = iname->len;
 		goto out;
 	}
-	ret = ext4_setup_fname_crypto(dir);
+	ret = ext4_get_encryption_info(dir);
 	if (ret)
 		return ret;
 	ci = EXT4_I(dir)->i_crypt_info;

fs/ext4/crypto_key.c +78 -30

index 858d7d6..442d24e 100644
@@ -84,20 +84,32 @@ out:
 	return res;
 }
 
-void ext4_free_encryption_info(struct inode *inode)
+void ext4_free_crypt_info(struct ext4_crypt_info *ci)
 {
-	struct ext4_inode_info *ei = EXT4_I(inode);
-	struct ext4_crypt_info *ci = ei->i_crypt_info;
-
 	if (!ci)
 		return;
 
 	if (ci->ci_keyring_key)
 		key_put(ci->ci_keyring_key);
 	crypto_free_ablkcipher(ci->ci_ctfm);
-	memzero_explicit(&ci->ci_raw, sizeof(ci->ci_raw));
 	kmem_cache_free(ext4_crypt_info_cachep, ci);
-	ei->i_crypt_info = NULL;
+}
+
+void ext4_free_encryption_info(struct inode *inode,
+			       struct ext4_crypt_info *ci)
+{
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	struct ext4_crypt_info *prev;
+
+	if (ci == NULL)
+		ci = ACCESS_ONCE(ei->i_crypt_info);
+	if (ci == NULL)
+		return;
+	prev = cmpxchg(&ei->i_crypt_info, ci, NULL);
+	if (prev != ci)
+		return;
+
+	ext4_free_crypt_info(ci);
 }
 
 int _ext4_get_encryption_info(struct inode *inode)

@@ -111,6 +123,10 @@ int _ext4_get_encryption_info(struct inode *inode)
 	struct ext4_encryption_context ctx;
 	struct user_key_payload *ukp;
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+	struct crypto_ablkcipher *ctfm;
+	const char *cipher_str;
+	char raw_key[EXT4_MAX_KEY_SIZE];
+	char mode;
 	int res;
 
 	if (!ext4_read_workqueue) {

@@ -119,11 +135,14 @@ int _ext4_get_encryption_info(struct inode *inode)
 			return res;
 	}
 
-	if (ei->i_crypt_info) {
-		if (!ei->i_crypt_info->ci_keyring_key ||
-		    key_validate(ei->i_crypt_info->ci_keyring_key) == 0)
+retry:
+	crypt_info = ACCESS_ONCE(ei->i_crypt_info);
+	if (crypt_info) {
+		if (!crypt_info->ci_keyring_key ||
+		    key_validate(crypt_info->ci_keyring_key) == 0)
 			return 0;
-		ext4_free_encryption_info(inode);
+		ext4_free_encryption_info(inode, crypt_info);
+		goto retry;
 	}
 
 	res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,

@@ -144,26 +163,37 @@ int _ext4_get_encryption_info(struct inode *inode)
 	if (!crypt_info)
 		return -ENOMEM;
 
-	ei->i_crypt_policy_flags = ctx.flags;
 	crypt_info->ci_flags = ctx.flags;
 	crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 	crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 	crypt_info->ci_ctfm = NULL;
+	crypt_info->ci_keyring_key = NULL;
 	memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 	       sizeof(crypt_info->ci_master_key));
 	if (S_ISREG(inode->i_mode))
-		crypt_info->ci_size =
-			ext4_encryption_key_size(crypt_info->ci_data_mode);
+		mode = crypt_info->ci_data_mode;
 	else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
-		crypt_info->ci_size =
-			ext4_encryption_key_size(crypt_info->ci_filename_mode);
+		mode = crypt_info->ci_filename_mode;
 	else
 		BUG();
-	BUG_ON(!crypt_info->ci_size);
-	if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
-		memset(crypt_info->ci_raw, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
+	switch (mode) {
+	case EXT4_ENCRYPTION_MODE_AES_256_XTS:
+		cipher_str = "xts(aes)";
+		break;
+	case EXT4_ENCRYPTION_MODE_AES_256_CTS:
+		cipher_str = "cts(cbc(aes))";
+		break;
+	default:
+		printk_once(KERN_WARNING
+			    "ext4: unsupported key mode %d (ino %u)\n",
+			    mode, (unsigned) inode->i_ino);
+		res = -ENOKEY;
 		goto out;
 	}
+	if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
+		memset(raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
+		goto got_key;
+	}
 	memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
 	       EXT4_KEY_DESC_PREFIX_SIZE);
 	sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,

@@ -177,6 +207,7 @@ int _ext4_get_encryption_info(struct inode *inode)
 		keyring_key = NULL;
 		goto out;
 	}
+	crypt_info->ci_keyring_key = keyring_key;
 	BUG_ON(keyring_key->type != &key_type_logon);
 	ukp = ((struct user_key_payload *)keyring_key->payload.data);
 	if (ukp->datalen != sizeof(struct ext4_encryption_key)) {

@@ -188,19 +219,36 @@ int _ext4_get_encryption_info(struct inode *inode)
 		     EXT4_KEY_DERIVATION_NONCE_SIZE);
 	BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
 	res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
-				  crypt_info->ci_raw);
-out:
-	if (res < 0) {
-		if (res == -ENOKEY)
-			res = 0;
-		kmem_cache_free(ext4_crypt_info_cachep, crypt_info);
-	} else {
-		ei->i_crypt_info = crypt_info;
-		crypt_info->ci_keyring_key = keyring_key;
-		keyring_key = NULL;
+				  raw_key);
+got_key:
+	ctfm = crypto_alloc_ablkcipher(cipher_str, 0, 0);
+	if (!ctfm || IS_ERR(ctfm)) {
+		res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
+		printk(KERN_DEBUG
+		       "%s: error %d (inode %u) allocating crypto tfm\n",
+		       __func__, res, (unsigned) inode->i_ino);
+		goto out;
+	}
+	crypt_info->ci_ctfm = ctfm;
+	crypto_ablkcipher_clear_flags(ctfm, ~0);
+	crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm),
+			     CRYPTO_TFM_REQ_WEAK_KEY);
+	res = crypto_ablkcipher_setkey(ctfm, raw_key,
+				       ext4_encryption_key_size(mode));
+	if (res)
+		goto out;
+	memzero_explicit(raw_key, sizeof(raw_key));
+	if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) != NULL) {
+		ext4_free_crypt_info(crypt_info);
+		goto retry;
 	}
-	if (keyring_key)
-		key_put(keyring_key);
+	return 0;
+
+out:
+	if (res == -ENOKEY)
+		res = 0;
+	ext4_free_crypt_info(crypt_info);
+	memzero_explicit(raw_key, sizeof(raw_key));
 	return res;
 }
 

fs/ext4/dir.c +0 -3

index 28cb94f..e11e6ae 100644
@@ -133,9 +133,6 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
 			return err;
 	}
 
-	err = ext4_setup_fname_crypto(inode);
-	if (err)
-		return err;
 	if (ext4_encrypted_inode(inode)) {
 		err = ext4_fname_crypto_alloc_buffer(inode, EXT4_NAME_LEN,
 						     &fname_crypto_str);

fs/ext4/ext4.h +2 -3

index 23e33fb..7435ff2 100644
@@ -911,7 +911,6 @@ struct ext4_inode_info {
 
 	/* on-disk additional length */
 	__u16 i_extra_isize;
-	char i_crypt_policy_flags;
 
 	/* Indicate the inline data space. */
 	u16 i_inline_off;

@@ -2105,7 +2104,6 @@ int ext4_fname_usr_to_disk(struct inode *inode,
 			   const struct qstr *iname,
 			   struct ext4_str *oname);
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
-int ext4_setup_fname_crypto(struct inode *inode);
 void ext4_fname_crypto_free_buffer(struct ext4_str *crypto_str);
 int ext4_fname_setup_filename(struct inode *dir, const struct qstr *iname,
 			      int lookup, struct ext4_filename *fname);

@@ -2131,7 +2129,8 @@ static inline void ext4_fname_free_filename(struct ext4_filename *fname) { }
 
 
 /* crypto_key.c */
-void ext4_free_encryption_info(struct inode *inode);
+void ext4_free_crypt_info(struct ext4_crypt_info *ci);
+void ext4_free_encryption_info(struct inode *inode, struct ext4_crypt_info *ci);
 int _ext4_get_encryption_info(struct inode *inode);
 
 #ifdef CONFIG_EXT4_FS_ENCRYPTION

fs/ext4/ext4_crypto.h +0 -3

index c5258f2..34e0d24 100644
@@ -74,13 +74,11 @@ struct ext4_encryption_key {
 } __attribute__((__packed__));
 
 struct ext4_crypt_info {
-	unsigned char	ci_size;
 	char		ci_data_mode;
 	char		ci_filename_mode;
 	char		ci_flags;
 	struct crypto_ablkcipher *ci_ctfm;
 	struct key	*ci_keyring_key;
-	char		ci_raw[EXT4_MAX_KEY_SIZE];
 	char		ci_master_key[EXT4_KEY_DESCRIPTOR_SIZE];
 };
 

@@ -89,7 +87,6 @@ struct ext4_crypt_info {
 #define EXT4_WRITE_PATH_FL			      0x00000004
 
 struct ext4_crypto_ctx {
-	struct crypto_tfm *tfm;         /* Crypto API context */
 	union {
 		struct {
 			struct page *bounce_page;       /* Ciphertext page */

fs/ext4/namei.c +9 -8

index 9bed99f..6ab50f8 100644
@@ -607,11 +607,12 @@ static struct stats dx_show_leaf(struct inode *dir,
 				char *name;
 				struct ext4_str fname_crypto_str
 					= {.name = NULL, .len = 0};
-				int res;
+				int res = 0;
 
 				name  = de->name;
 				len = de->name_len;
-				res = ext4_setup_fname_crypto(dir);
+				if (ext4_encrypted_inode(inode))
+					res = ext4_get_encryption_info(dir);
 				if (res) {
 					printk(KERN_WARNING "Error setting up"
 					       " fname crypto: %d\n", res);

@@ -953,12 +954,12 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 					   EXT4_DIR_REC_LEN(0));
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 	/* Check if the directory is encrypted */
-	err = ext4_setup_fname_crypto(dir);
-	if (err) {
-		brelse(bh);
-		return err;
-	}
 	if (ext4_encrypted_inode(dir)) {
+		err = ext4_get_encryption_info(dir);
+		if (err < 0) {
+			brelse(bh);
+			return err;
+		}
 		err = ext4_fname_crypto_alloc_buffer(dir, EXT4_NAME_LEN,
 						     &fname_crypto_str);
 		if (err < 0) {

@@ -3108,7 +3109,7 @@ static int ext4_symlink(struct inode *dir,
 		err = ext4_inherit_context(dir, inode);
 		if (err)
 			goto err_drop_inode;
-		err = ext4_setup_fname_crypto(inode);
+		err = ext4_get_encryption_info(inode);
 		if (err)
 			goto err_drop_inode;
 		istr.name = (const unsigned char *) symname;

fs/ext4/super.c +1 -1

index b0bd1c1..56bfc2f 100644
@@ -959,7 +959,7 @@ void ext4_clear_inode(struct inode *inode)
 	}
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 	if (EXT4_I(inode)->i_crypt_info)
-		ext4_free_encryption_info(inode);
+		ext4_free_encryption_info(inode, EXT4_I(inode)->i_crypt_info);
 #endif
 }
 

fs/ext4/symlink.c +1 -1

index 3287088..68e915a 100644
@@ -37,7 +37,7 @@ static void *ext4_follow_link(struct dentry *dentry, struct nameidata *nd)
 	if (!ext4_encrypted_inode(inode))
 		return page_follow_link_light(dentry, nd);
 
-	res = ext4_setup_fname_crypto(inode);
+	res = ext4_get_encryption_info(inode);
 	if (res)
 		return ERR_PTR(res);
 

Signature · 1 line

2.3.0

Looking at a glance, it's mostly same as what I wanted. The key is to share ci->ci_ctfm for regular file and the other dir/symlink files. So, ext4_get_encryption_info will handle most of cases.

In ext4_readdir, it also needs ext4_get_encryption_info?

Quoted 5 lines · Jaegeuk Kim

Previoulsy, fi->i_crypt_info was not covered by any lock, resulting in memory leak.

This patch adds a rwsem to avoid leaking objects on i_crypt_info.

Quoted 1 line

Signed-off-by Jaegeuk Kim <[email protected]>

I'm not sure we need an rwsem to fix this issue. In terms of serializing the creation and deletion of the structure, it should be possible to use an cmpxchg() on the pointer itself. (e.g., if we lose the race on the creation side, we just release our structure and use the one that the winner allocated).

If we do end up needing to serialize access to the tfm in the i_crypt_info object for datapath reads/writes, then we might need a mutex, but I think that should be it, no?