Re: [f2fs-dev] [PATCH] f2fs crypto: add rwsem to avoid data races
From: Jaegeuk Kim
Date: Wed May 20 2015 - 00:56:22 EST
On Wed, May 20, 2015 at 12:35:18AM -0400, Theodore Ts'o wrote:
> On Tue, May 19, 2015 at 05:38:59PM -0700, Jaegeuk Kim wrote:
> >
> > 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.
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?
Using cmpxchg is really cool to me.
I'll test this too in f2fs tomorrow.
Thanks,
>
> - Ted
>
> >From 6a57d7bbf7bd2d31432e55f266543bb56bf7e1fc Mon Sep 17 00:00:00 2001
> From: Theodore Ts'o <tytso@xxxxxxx>
> 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 <tytso@xxxxxxx>
> ---
> 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(-)
>
> diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
> index 1484b58..68c7ab8 100644
> --- a/fs/ext4/crypto.c
> +++ b/fs/ext4/crypto.c
> @@ -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",
> diff --git a/fs/ext4/crypto_fname.c b/fs/ext4/crypto_fname.c
> index e63dd29..29a2dc9 100644
> --- a/fs/ext4/crypto_fname.c
> +++ b/fs/ext4/crypto_fname.c
> @@ -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;
> diff --git a/fs/ext4/crypto_key.c b/fs/ext4/crypto_key.c
> index 858d7d6..442d24e 100644
> --- a/fs/ext4/crypto_key.c
> +++ b/fs/ext4/crypto_key.c
> @@ -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;
> }
>
> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
> index 28cb94f..e11e6ae 100644
> --- a/fs/ext4/dir.c
> +++ b/fs/ext4/dir.c
> @@ -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);
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 23e33fb..7435ff2 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -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
> diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
> index c5258f2..34e0d24 100644
> --- a/fs/ext4/ext4_crypto.h
> +++ b/fs/ext4/ext4_crypto.h
> @@ -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 */
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 9bed99f..6ab50f8 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -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;
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index b0bd1c1..56bfc2f 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -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
> }
>
> diff --git a/fs/ext4/symlink.c b/fs/ext4/symlink.c
> index 3287088..68e915a 100644
> --- a/fs/ext4/symlink.c
> +++ b/fs/ext4/symlink.c
> @@ -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);
>
> --
> 2.3.0
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