fscrypt: support test_dummy_encryption=v2

v1 encryption policies are deprecated in favor of v2, and some new
features (e.g. encryption+casefolding) are only being added for v2.

Therefore, the "test_dummy_encryption" mount option (which is used for
encryption I/O testing with xfstests) needs to support v2 policies.

To do this, extend its syntax to be "test_dummy_encryption=v1" or
"test_dummy_encryption=v2".  The existing "test_dummy_encryption" (no
argument) also continues to be accepted, to specify the default setting
-- currently v1, but the next patch changes it to v2.

To cleanly support both v1 and v2 while also making it easy to support
specifying other encryption settings in the future (say, accepting
"$contents_mode:$filenames_mode:v2"), make ext4 and f2fs maintain a
pointer to the dummy fscrypt_context rather than using mount flags.

To avoid concurrency issues, don't allow test_dummy_encryption to be set
or changed during a remount.  (The former restriction is new, but
xfstests doesn't run into it, so no one should notice.)

Tested with 'gce-xfstests -c {ext4,f2fs}/encrypt -g auto'.  On ext4,
there are two regressions, both of which are test bugs: ext4/023 and
ext4/028 fail because they set an xattr and expect it to be stored
inline, but the increase in size of the fscrypt_context from
24 to 40 bytes causes this xattr to be spilled into an external block.

Link: https://lore.kernel.org/r/20200512233251.118314-4-ebiggers@kernel.org
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>

10 files changed, 307 insertions, 60 deletions

diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index 87d794bc75a4..4218ac658629 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/Documentation/filesystems/f2fs.rst
@@ -225,8 +225,12 @@ fsync_mode=%s          Control the policy of fsync. Currently supports "posix",
                        pass, but the performance will regress. "nobarrier" is
                        based on "posix", but doesn't issue flush command for
                        non-atomic files likewise "nobarrier" mount option.
-test_dummy_encryption  Enable dummy encryption, which provides a fake fscrypt
+test_dummy_encryption
+test_dummy_encryption=%s
+                       Enable dummy encryption, which provides a fake fscrypt
                        context. The fake fscrypt context is used by xfstests.
+                       The argument may be either "v1" or "v2", in order to
+                       select the corresponding fscrypt policy version.
 checkpoint=%s[:%u[%]]  Set to "disable" to turn off checkpointing. Set to "enable"
                        to reenable checkpointing. Is enabled by default. While
                        disabled, any unmounting or unexpected shutdowns will cause
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index edc4590c69f0..675479f8e6f3 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -395,21 +395,18 @@ int fscrypt_get_encryption_info(struct inode *inode)
 
 	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 	if (res < 0) {
-		if (!fscrypt_dummy_context_enabled(inode) ||
-		    IS_ENCRYPTED(inode)) {
+		const union fscrypt_context *dummy_ctx =
+			fscrypt_get_dummy_context(inode->i_sb);
+
+		if (IS_ENCRYPTED(inode) || !dummy_ctx) {
 			fscrypt_warn(inode,
 				     "Error %d getting encryption context",
 				     res);
 			return res;
 		}
 		/* Fake up a context for an unencrypted directory */
-		memset(&ctx, 0, sizeof(ctx));
-		ctx.version = FSCRYPT_CONTEXT_V1;
-		ctx.v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
-		ctx.v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
-		memset(ctx.v1.master_key_descriptor, 0x42,
-		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-		res = sizeof(ctx.v1);
+		res = fscrypt_context_size(dummy_ctx);
+		memcpy(&ctx, dummy_ctx, res);
 	}
 
 	crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 0a95537fcef9..bcab94b29d10 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -11,6 +11,7 @@
  */
 
 #include <linux/random.h>
+#include <linux/seq_file.h>
 #include <linux/string.h>
 #include <linux/mount.h>
 #include "fscrypt_private.h"
@@ -616,3 +617,127 @@ int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 	return preload ? fscrypt_get_encryption_info(child): 0;
 }
 EXPORT_SYMBOL(fscrypt_inherit_context);
+
+/**
+ * fscrypt_set_test_dummy_encryption() - handle '-o test_dummy_encryption'
+ * @sb: the filesystem on which test_dummy_encryption is being specified
+ * @arg: the argument to the test_dummy_encryption option.
+ *	 If no argument was specified, then @arg->from == NULL.
+ * @dummy_ctx: the filesystem's current dummy context (input/output, see below)
+ *
+ * Handle the test_dummy_encryption mount option by creating a dummy encryption
+ * context, saving it in @dummy_ctx, and adding the corresponding dummy
+ * encryption key to the filesystem.  If the @dummy_ctx is already set, then
+ * instead validate that it matches @arg.  Don't support changing it via
+ * remount, as that is difficult to do safely.
+ *
+ * The reason we use an fscrypt_context rather than an fscrypt_policy is because
+ * we mustn't generate a new nonce each time we access a dummy-encrypted
+ * directory, as that would change the way filenames are encrypted.
+ *
+ * Return: 0 on success (dummy context set, or the same context is already set);
+ *         -EEXIST if a different dummy context is already set;
+ *         or another -errno value.
+ */
+int fscrypt_set_test_dummy_encryption(struct super_block *sb,
+				      const substring_t *arg,
+				      struct fscrypt_dummy_context *dummy_ctx)
+{
+	const char *argstr = "v1";
+	const char *argstr_to_free = NULL;
+	struct fscrypt_key_specifier key_spec = { 0 };
+	int version;
+	union fscrypt_context *ctx = NULL;
+	int err;
+
+	if (arg->from) {
+		argstr = argstr_to_free = match_strdup(arg);
+		if (!argstr)
+			return -ENOMEM;
+	}
+
+	if (!strcmp(argstr, "v1")) {
+		version = FSCRYPT_CONTEXT_V1;
+		key_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
+		memset(key_spec.u.descriptor, 0x42,
+		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	} else if (!strcmp(argstr, "v2")) {
+		version = FSCRYPT_CONTEXT_V2;
+		key_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
+		/* key_spec.u.identifier gets filled in when adding the key */
+	} else {
+		err = -EINVAL;
+		goto out;
+	}
+
+	if (dummy_ctx->ctx) {
+		/*
+		 * Note: if we ever make test_dummy_encryption support
+		 * specifying other encryption settings, such as the encryption
+		 * modes, we'll need to compare those settings here.
+		 */
+		if (dummy_ctx->ctx->version == version)
+			err = 0;
+		else
+			err = -EEXIST;
+		goto out;
+	}
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	err = fscrypt_add_test_dummy_key(sb, &key_spec);
+	if (err)
+		goto out;
+
+	ctx->version = version;
+	switch (ctx->version) {
+	case FSCRYPT_CONTEXT_V1:
+		ctx->v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
+		ctx->v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
+		memcpy(ctx->v1.master_key_descriptor, key_spec.u.descriptor,
+		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+		break;
+	case FSCRYPT_CONTEXT_V2:
+		ctx->v2.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
+		ctx->v2.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
+		memcpy(ctx->v2.master_key_identifier, key_spec.u.identifier,
+		       FSCRYPT_KEY_IDENTIFIER_SIZE);
+		break;
+	default:
+		WARN_ON(1);
+		err = -EINVAL;
+		goto out;
+	}
+	dummy_ctx->ctx = ctx;
+	ctx = NULL;
+	err = 0;
+out:
+	kfree(ctx);
+	kfree(argstr_to_free);
+	return err;
+}
+EXPORT_SYMBOL_GPL(fscrypt_set_test_dummy_encryption);
+
+/**
+ * fscrypt_show_test_dummy_encryption() - show '-o test_dummy_encryption'
+ * @seq: the seq_file to print the option to
+ * @sep: the separator character to use
+ * @sb: the filesystem whose options are being shown
+ *
+ * Show the test_dummy_encryption mount option, if it was specified.
+ * This is mainly used for /proc/mounts.
+ */
+void fscrypt_show_test_dummy_encryption(struct seq_file *seq, char sep,
+					struct super_block *sb)
+{
+	const union fscrypt_context *ctx = fscrypt_get_dummy_context(sb);
+
+	if (!ctx)
+		return;
+	seq_printf(seq, "%ctest_dummy_encryption=v%d", sep, ctx->version);
+}
+EXPORT_SYMBOL_GPL(fscrypt_show_test_dummy_encryption);
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 91eb4381cae5..546504cba842 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1357,11 +1357,9 @@ struct ext4_super_block {
  */
 #define EXT4_MF_MNTDIR_SAMPLED		0x0001
 #define EXT4_MF_FS_ABORTED		0x0002	/* Fatal error detected */
-#define EXT4_MF_TEST_DUMMY_ENCRYPTION	0x0004
 
 #ifdef CONFIG_FS_ENCRYPTION
-#define DUMMY_ENCRYPTION_ENABLED(sbi) (unlikely((sbi)->s_mount_flags & \
-						EXT4_MF_TEST_DUMMY_ENCRYPTION))
+#define DUMMY_ENCRYPTION_ENABLED(sbi) ((sbi)->s_dummy_enc_ctx.ctx != NULL)
 #else
 #define DUMMY_ENCRYPTION_ENABLED(sbi) (0)
 #endif
@@ -1551,6 +1549,9 @@ struct ext4_sb_info {
 	struct ratelimit_state s_warning_ratelimit_state;
 	struct ratelimit_state s_msg_ratelimit_state;
 
+	/* Encryption context for '-o test_dummy_encryption' */
+	struct fscrypt_dummy_context s_dummy_enc_ctx;
+
 	/*
 	 * Barrier between writepages ops and changing any inode's JOURNAL_DATA
 	 * or EXTENTS flag.
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index bf5fcb477f66..4a3d21972011 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1106,6 +1106,7 @@ static void ext4_put_super(struct super_block *sb)
 		crypto_free_shash(sbi->s_chksum_driver);
 	kfree(sbi->s_blockgroup_lock);
 	fs_put_dax(sbi->s_daxdev);
+	fscrypt_free_dummy_context(&sbi->s_dummy_enc_ctx);
 #ifdef CONFIG_UNICODE
 	utf8_unload(sbi->s_encoding);
 #endif
@@ -1389,9 +1390,10 @@ retry:
 	return res;
 }
 
-static bool ext4_dummy_context(struct inode *inode)
+static const union fscrypt_context *
+ext4_get_dummy_context(struct super_block *sb)
 {
-	return DUMMY_ENCRYPTION_ENABLED(EXT4_SB(inode->i_sb));
+	return EXT4_SB(sb)->s_dummy_enc_ctx.ctx;
 }
 
 static bool ext4_has_stable_inodes(struct super_block *sb)
@@ -1410,7 +1412,7 @@ static const struct fscrypt_operations ext4_cryptops = {
 	.key_prefix		= "ext4:",
 	.get_context		= ext4_get_context,
 	.set_context		= ext4_set_context,
-	.dummy_context		= ext4_dummy_context,
+	.get_dummy_context	= ext4_get_dummy_context,
 	.empty_dir		= ext4_empty_dir,
 	.max_namelen		= EXT4_NAME_LEN,
 	.has_stable_inodes	= ext4_has_stable_inodes,
@@ -1605,6 +1607,7 @@ static const match_table_t tokens = {
 	{Opt_init_itable, "init_itable"},
 	{Opt_noinit_itable, "noinit_itable"},
 	{Opt_max_dir_size_kb, "max_dir_size_kb=%u"},
+	{Opt_test_dummy_encryption, "test_dummy_encryption=%s"},
 	{Opt_test_dummy_encryption, "test_dummy_encryption"},
 	{Opt_nombcache, "nombcache"},
 	{Opt_nombcache, "no_mbcache"},	/* for backward compatibility */
@@ -1816,7 +1819,7 @@ static const struct mount_opts {
 	{Opt_jqfmt_vfsv0, QFMT_VFS_V0, MOPT_QFMT},
 	{Opt_jqfmt_vfsv1, QFMT_VFS_V1, MOPT_QFMT},
 	{Opt_max_dir_size_kb, 0, MOPT_GTE0},
-	{Opt_test_dummy_encryption, 0, MOPT_GTE0},
+	{Opt_test_dummy_encryption, 0, MOPT_STRING},
 	{Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
 	{Opt_err, 0, 0}
 };
@@ -1851,6 +1854,48 @@ static int ext4_sb_read_encoding(const struct ext4_super_block *es,
 }
 #endif
 
+static int ext4_set_test_dummy_encryption(struct super_block *sb,
+					  const char *opt,
+					  const substring_t *arg,
+					  bool is_remount)
+{
+#ifdef CONFIG_FS_ENCRYPTION
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	int err;
+
+	/*
+	 * This mount option is just for testing, and it's not worthwhile to
+	 * implement the extra complexity (e.g. RCU protection) that would be
+	 * needed to allow it to be set or changed during remount.  We do allow
+	 * it to be specified during remount, but only if there is no change.
+	 */
+	if (is_remount && !sbi->s_dummy_enc_ctx.ctx) {
+		ext4_msg(sb, KERN_WARNING,
+			 "Can't set test_dummy_encryption on remount");
+		return -1;
+	}
+	err = fscrypt_set_test_dummy_encryption(sb, arg, &sbi->s_dummy_enc_ctx);
+	if (err) {
+		if (err == -EEXIST)
+			ext4_msg(sb, KERN_WARNING,
+				 "Can't change test_dummy_encryption on remount");
+		else if (err == -EINVAL)
+			ext4_msg(sb, KERN_WARNING,
+				 "Value of option \"%s\" is unrecognized", opt);
+		else
+			ext4_msg(sb, KERN_WARNING,
+				 "Error processing option \"%s\" [%d]",
+				 opt, err);
+		return -1;
+	}
+	ext4_msg(sb, KERN_WARNING, "Test dummy encryption mode enabled");
+#else
+	ext4_msg(sb, KERN_WARNING,
+		 "Test dummy encryption mount option ignored");
+#endif
+	return 1;
+}
+
 static int handle_mount_opt(struct super_block *sb, char *opt, int token,
 			    substring_t *args, unsigned long *journal_devnum,
 			    unsigned int *journal_ioprio, int is_remount)
@@ -2047,14 +2092,8 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
 		*journal_ioprio =
 			IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, arg);
 	} else if (token == Opt_test_dummy_encryption) {
-#ifdef CONFIG_FS_ENCRYPTION
-		sbi->s_mount_flags |= EXT4_MF_TEST_DUMMY_ENCRYPTION;
-		ext4_msg(sb, KERN_WARNING,
-			 "Test dummy encryption mode enabled");
-#else
-		ext4_msg(sb, KERN_WARNING,
-			 "Test dummy encryption mount option ignored");
-#endif
+		return ext4_set_test_dummy_encryption(sb, opt, &args[0],
+						      is_remount);
 	} else if (m->flags & MOPT_DATAJ) {
 		if (is_remount) {
 			if (!sbi->s_journal)
@@ -2311,8 +2350,8 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
 		SEQ_OPTS_PRINT("max_dir_size_kb=%u", sbi->s_max_dir_size_kb);
 	if (test_opt(sb, DATA_ERR_ABORT))
 		SEQ_OPTS_PUTS("data_err=abort");
-	if (DUMMY_ENCRYPTION_ENABLED(sbi))
-		SEQ_OPTS_PUTS("test_dummy_encryption");
+
+	fscrypt_show_test_dummy_encryption(seq, sep, sb);
 
 	ext4_show_quota_options(seq, sb);
 	return 0;
@@ -4780,6 +4819,7 @@ failed_mount:
 	for (i = 0; i < EXT4_MAXQUOTAS; i++)
 		kfree(get_qf_name(sb, sbi, i));
 #endif
+	fscrypt_free_dummy_context(&sbi->s_dummy_enc_ctx);
 	ext4_blkdev_remove(sbi);
 	brelse(bh);
 out_fail:
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index 04bfaf63752c..6c9fc9e21c13 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -293,6 +293,7 @@ EXT4_ATTR_FEATURE(batched_discard);
 EXT4_ATTR_FEATURE(meta_bg_resize);
 #ifdef CONFIG_FS_ENCRYPTION
 EXT4_ATTR_FEATURE(encryption);
+EXT4_ATTR_FEATURE(test_dummy_encryption_v2);
 #endif
 #ifdef CONFIG_UNICODE
 EXT4_ATTR_FEATURE(casefold);
@@ -308,6 +309,7 @@ static struct attribute *ext4_feat_attrs[] = {
 	ATTR_LIST(meta_bg_resize),
 #ifdef CONFIG_FS_ENCRYPTION
 	ATTR_LIST(encryption),
+	ATTR_LIST(test_dummy_encryption_v2),
 #endif
 #ifdef CONFIG_UNICODE
 	ATTR_LIST(casefold),
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index ba470d5687fe..157eec348970 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -138,7 +138,7 @@ struct f2fs_mount_info {
 	int fsync_mode;			/* fsync policy */
 	int fs_mode;			/* fs mode: LFS or ADAPTIVE */
 	int bggc_mode;			/* bggc mode: off, on or sync */
-	bool test_dummy_encryption;	/* test dummy encryption */
+	struct fscrypt_dummy_context dummy_enc_ctx; /* test dummy encryption */
 	block_t unusable_cap;		/* Amount of space allowed to be
 					 * unusable when disabling checkpoint
 					 */
@@ -1259,7 +1259,7 @@ enum fsync_mode {
 
 #ifdef CONFIG_FS_ENCRYPTION
 #define DUMMY_ENCRYPTION_ENABLED(sbi) \
-			(unlikely(F2FS_OPTION(sbi).test_dummy_encryption))
+	(unlikely(F2FS_OPTION(sbi).dummy_enc_ctx.ctx != NULL))
 #else
 #define DUMMY_ENCRYPTION_ENABLED(sbi) (0)
 #endif
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index f2dfc21c6abb..8a9955902d84 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -202,6 +202,7 @@ static match_table_t f2fs_tokens = {
 	{Opt_whint, "whint_mode=%s"},
 	{Opt_alloc, "alloc_mode=%s"},
 	{Opt_fsync, "fsync_mode=%s"},
+	{Opt_test_dummy_encryption, "test_dummy_encryption=%s"},
 	{Opt_test_dummy_encryption, "test_dummy_encryption"},
 	{Opt_checkpoint_disable, "checkpoint=disable"},
 	{Opt_checkpoint_disable_cap, "checkpoint=disable:%u"},
@@ -394,7 +395,52 @@ static int f2fs_check_quota_options(struct f2fs_sb_info *sbi)
 }
 #endif
 
-static int parse_options(struct super_block *sb, char *options)
+static int f2fs_set_test_dummy_encryption(struct super_block *sb,
+					  const char *opt,
+					  const substring_t *arg,
+					  bool is_remount)
+{
+	struct f2fs_sb_info *sbi = F2FS_SB(sb);
+#ifdef CONFIG_FS_ENCRYPTION
+	int err;
+
+	if (!f2fs_sb_has_encrypt(sbi)) {
+		f2fs_err(sbi, "Encrypt feature is off");
+		return -EINVAL;
+	}
+
+	/*
+	 * This mount option is just for testing, and it's not worthwhile to
+	 * implement the extra complexity (e.g. RCU protection) that would be
+	 * needed to allow it to be set or changed during remount.  We do allow
+	 * it to be specified during remount, but only if there is no change.
+	 */
+	if (is_remount && !F2FS_OPTION(sbi).dummy_enc_ctx.ctx) {
+		f2fs_warn(sbi, "Can't set test_dummy_encryption on remount");
+		return -EINVAL;
+	}
+	err = fscrypt_set_test_dummy_encryption(
+		sb, arg, &F2FS_OPTION(sbi).dummy_enc_ctx);
+	if (err) {
+		if (err == -EEXIST)
+			f2fs_warn(sbi,
+				  "Can't change test_dummy_encryption on remount");
+		else if (err == -EINVAL)
+			f2fs_warn(sbi, "Value of option \"%s\" is unrecognized",
+				  opt);
+		else
+			f2fs_warn(sbi, "Error processing option \"%s\" [%d]",
+				  opt, err);
+		return -EINVAL;
+	}
+	f2fs_warn(sbi, "Test dummy encryption mode enabled");
+#else
+	f2fs_warn(sbi, "Test dummy encryption mount option ignored");
+#endif
+	return 0;
+}
+
+static int parse_options(struct super_block *sb, char *options, bool is_remount)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(sb);
 	substring_t args[MAX_OPT_ARGS];
@@ -403,9 +449,7 @@ static int parse_options(struct super_block *sb, char *options)
 	int arg = 0, ext_cnt;
 	kuid_t uid;
 	kgid_t gid;
-#ifdef CONFIG_QUOTA
 	int ret;
-#endif
 
 	if (!options)
 		return 0;
@@ -778,17 +822,10 @@ static int parse_options(struct super_block *sb, char *options)
 			kvfree(name);
 			break;
 		case Opt_test_dummy_encryption:
-#ifdef CONFIG_FS_ENCRYPTION
-			if (!f2fs_sb_has_encrypt(sbi)) {
-				f2fs_err(sbi, "Encrypt feature is off");
-				return -EINVAL;
-			}
-
-			F2FS_OPTION(sbi).test_dummy_encryption = true;
-			f2fs_info(sbi, "Test dummy encryption mode enabled");
-#else
-			f2fs_info(sbi, "Test dummy encryption mount option ignored");
-#endif
+			ret = f2fs_set_test_dummy_encryption(sb, p, &args[0],
+							     is_remount);
+			if (ret)
+				return ret;
 			break;
 		case Opt_checkpoint_disable_cap_perc:
 			if (args->from && match_int(args, &arg))
@@ -1213,6 +1250,7 @@ static void f2fs_put_super(struct super_block *sb)
 	for (i = 0; i < MAXQUOTAS; i++)
 		kvfree(F2FS_OPTION(sbi).s_qf_names[i]);
 #endif
+	fscrypt_free_dummy_context(&F2FS_OPTION(sbi).dummy_enc_ctx);
 	destroy_percpu_info(sbi);
 	for (i = 0; i < NR_PAGE_TYPE; i++)
 		kvfree(sbi->write_io[i]);
@@ -1543,10 +1581,8 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 		seq_printf(seq, ",whint_mode=%s", "user-based");
 	else if (F2FS_OPTION(sbi).whint_mode == WHINT_MODE_FS)
 		seq_printf(seq, ",whint_mode=%s", "fs-based");
-#ifdef CONFIG_FS_ENCRYPTION
-	if (F2FS_OPTION(sbi).test_dummy_encryption)
-		seq_puts(seq, ",test_dummy_encryption");
-#endif
+
+	fscrypt_show_test_dummy_encryption(seq, ',', sbi->sb);
 
 	if (F2FS_OPTION(sbi).alloc_mode == ALLOC_MODE_DEFAULT)
 		seq_printf(seq, ",alloc_mode=%s", "default");
@@ -1575,7 +1611,6 @@ static void default_options(struct f2fs_sb_info *sbi)
 	F2FS_OPTION(sbi).whint_mode = WHINT_MODE_OFF;
 	F2FS_OPTION(sbi).alloc_mode = ALLOC_MODE_DEFAULT;
 	F2FS_OPTION(sbi).fsync_mode = FSYNC_MODE_POSIX;
-	F2FS_OPTION(sbi).test_dummy_encryption = false;
 	F2FS_OPTION(sbi).s_resuid = make_kuid(&init_user_ns, F2FS_DEF_RESUID);
 	F2FS_OPTION(sbi).s_resgid = make_kgid(&init_user_ns, F2FS_DEF_RESGID);
 	F2FS_OPTION(sbi).compress_algorithm = COMPRESS_LZ4;
@@ -1734,7 +1769,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	default_options(sbi);
 
 	/* parse mount options */
-	err = parse_options(sb, data);
+	err = parse_options(sb, data, true);
 	if (err)
 		goto restore_opts;
 	checkpoint_changed =
@@ -2410,9 +2445,10 @@ static int f2fs_set_context(struct inode *inode, const void *ctx, size_t len,
 				ctx, len, fs_data, XATTR_CREATE);
 }
 
-static bool f2fs_dummy_context(struct inode *inode)
+static const union fscrypt_context *
+f2fs_get_dummy_context(struct super_block *sb)
 {
-	return DUMMY_ENCRYPTION_ENABLED(F2FS_I_SB(inode));
+	return F2FS_OPTION(F2FS_SB(sb)).dummy_enc_ctx.ctx;
 }
 
 static bool f2fs_has_stable_inodes(struct super_block *sb)
@@ -2431,7 +2467,7 @@ static const struct fscrypt_operations f2fs_cryptops = {
 	.key_prefix		= "f2fs:",
 	.get_context		= f2fs_get_context,
 	.set_context		= f2fs_set_context,
-	.dummy_context		= f2fs_dummy_context,
+	.get_dummy_context	= f2fs_get_dummy_context,
 	.empty_dir		= f2fs_empty_dir,
 	.max_namelen		= F2FS_NAME_LEN,
 	.has_stable_inodes	= f2fs_has_stable_inodes,
@@ -3366,7 +3402,7 @@ try_onemore:
 		goto free_sb_buf;
 	}
 
-	err = parse_options(sb, options);
+	err = parse_options(sb, options, false);
 	if (err)
 		goto free_options;
 
@@ -3769,6 +3805,7 @@ free_options:
 	for (i = 0; i < MAXQUOTAS; i++)
 		kvfree(F2FS_OPTION(sbi).s_qf_names[i]);
 #endif
+	fscrypt_free_dummy_context(&F2FS_OPTION(sbi).dummy_enc_ctx);
 	kvfree(options);
 free_sb_buf:
 	kvfree(raw_super);
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index e3bbbef9b4f0..3162f46b3c9b 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -446,6 +446,7 @@ enum feat_id {
 	FEAT_SB_CHECKSUM,
 	FEAT_CASEFOLD,
 	FEAT_COMPRESSION,
+	FEAT_TEST_DUMMY_ENCRYPTION_V2,
 };
 
 static ssize_t f2fs_feature_show(struct f2fs_attr *a,
@@ -466,6 +467,7 @@ static ssize_t f2fs_feature_show(struct f2fs_attr *a,
 	case FEAT_SB_CHECKSUM:
 	case FEAT_CASEFOLD:
 	case FEAT_COMPRESSION:
+	case FEAT_TEST_DUMMY_ENCRYPTION_V2:
 		return sprintf(buf, "supported\n");
 	}
 	return 0;
@@ -563,6 +565,7 @@ F2FS_GENERAL_RO_ATTR(avg_vblocks);
 
 #ifdef CONFIG_FS_ENCRYPTION
 F2FS_FEATURE_RO_ATTR(encryption, FEAT_CRYPTO);
+F2FS_FEATURE_RO_ATTR(test_dummy_encryption_v2, FEAT_TEST_DUMMY_ENCRYPTION_V2);
 #endif
 #ifdef CONFIG_BLK_DEV_ZONED
 F2FS_FEATURE_RO_ATTR(block_zoned, FEAT_BLKZONED);
@@ -647,6 +650,7 @@ ATTRIBUTE_GROUPS(f2fs);
 static struct attribute *f2fs_feat_attrs[] = {
 #ifdef CONFIG_FS_ENCRYPTION
 	ATTR_LIST(encryption),
+	ATTR_LIST(test_dummy_encryption_v2),
 #endif
 #ifdef CONFIG_BLK_DEV_ZONED
 	ATTR_LIST(block_zoned),
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 0e0c7ad19383..2862ca5fea33 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -15,12 +15,15 @@
 
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/parser.h>
 #include <linux/slab.h>
 #include <uapi/linux/fscrypt.h>
 
 #define FS_CRYPTO_BLOCK_SIZE		16
 
+union fscrypt_context;
 struct fscrypt_info;
+struct seq_file;
 
 struct fscrypt_str {
 	unsigned char *name;
@@ -59,7 +62,8 @@ struct fscrypt_operations {
 	int (*get_context)(struct inode *inode, void *ctx, size_t len);
 	int (*set_context)(struct inode *inode, const void *ctx, size_t len,
 			   void *fs_data);
-	bool (*dummy_context)(struct inode *inode);
+	const union fscrypt_context *(*get_dummy_context)(
+		struct super_block *sb);
 	bool (*empty_dir)(struct inode *inode);
 	unsigned int max_namelen;
 	bool (*has_stable_inodes)(struct super_block *sb);
@@ -89,10 +93,12 @@ static inline bool fscrypt_needs_contents_encryption(const struct inode *inode)
 	return IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode);
 }
 
-static inline bool fscrypt_dummy_context_enabled(struct inode *inode)
+static inline const union fscrypt_context *
+fscrypt_get_dummy_context(struct super_block *sb)
 {
-	return inode->i_sb->s_cop->dummy_context &&
-		inode->i_sb->s_cop->dummy_context(inode);
+	if (!sb->s_cop->get_dummy_context)
+		return NULL;
+	return sb->s_cop->get_dummy_context(sb);
 }
 
 /*
@@ -145,6 +151,22 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child);
 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 			    void *fs_data, bool preload);
 
+struct fscrypt_dummy_context {
+	const union fscrypt_context *ctx;
+};
+
+int fscrypt_set_test_dummy_encryption(struct super_block *sb,
+				      const substring_t *arg,
+				      struct fscrypt_dummy_context *dummy_ctx);
+void fscrypt_show_test_dummy_encryption(struct seq_file *seq, char sep,
+					struct super_block *sb);
+static inline void
+fscrypt_free_dummy_context(struct fscrypt_dummy_context *dummy_ctx)
+{
+	kfree(dummy_ctx->ctx);
+	dummy_ctx->ctx = NULL;
+}
+
 /* keyring.c */
 void fscrypt_sb_free(struct super_block *sb);
 int fscrypt_ioctl_add_key(struct file *filp, void __user *arg);
@@ -219,9 +241,10 @@ static inline bool fscrypt_needs_contents_encryption(const struct inode *inode)
 	return false;
 }
 
-static inline bool fscrypt_dummy_context_enabled(struct inode *inode)
+static inline const union fscrypt_context *
+fscrypt_get_dummy_context(struct super_block *sb)
 {
-	return false;
+	return NULL;
 }
 
 static inline void fscrypt_handle_d_move(struct dentry *dentry)
@@ -316,6 +339,20 @@ static inline int fscrypt_inherit_context(struct inode *parent,
 	return -EOPNOTSUPP;
 }
 
+struct fscrypt_dummy_context {
+};
+
+static inline void fscrypt_show_test_dummy_encryption(struct seq_file *seq,
+						      char sep,
+						      struct super_block *sb)
+{
+}
+
+static inline void
+fscrypt_free_dummy_context(struct fscrypt_dummy_context *dummy_ctx)
+{
+}
+
 /* keyring.c */
 static inline void fscrypt_sb_free(struct super_block *sb)
 {
@@ -677,7 +714,7 @@ static inline int fscrypt_prepare_symlink(struct inode *dir,
 					  unsigned int max_len,
 					  struct fscrypt_str *disk_link)
 {
-	if (IS_ENCRYPTED(dir) || fscrypt_dummy_context_enabled(dir))
+	if (IS_ENCRYPTED(dir) || fscrypt_get_dummy_context(dir->i_sb) != NULL)
 		return __fscrypt_prepare_symlink(dir, len, max_len, disk_link);
 
 	disk_link->name = (unsigned char *)target;