Re: [PATCH v3 13/13] fscrypt: make fscrypt_set_test_dummy_encryption() take a 'const char *'

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2020-09-16 at 21:11 -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> fscrypt_set_test_dummy_encryption() requires that the optional argument
> to the test_dummy_encryption mount option be specified as a substring_t.
> That doesn't work well with filesystems that use the new mount API,
> since the new way of parsing mount options doesn't use substring_t.
> 
> Make it take the argument as a 'const char *' instead.
> 
> Instead of moving the match_strdup() into the callers in ext4 and f2fs,
> make them just use arg->from directly.  Since the pattern is
> "test_dummy_encryption=%s", the argument will be null-terminated.
> 

Are you sure about that? I thought the point of substring_t was to give
you a token from the string without null terminating it.

ISTM that when you just pass in ->from, you might end up with trailing
arguments in your string like this. e.g.:

    "v2,foo,bar,baz"

...and then that might fail to match properly
in fscrypt_set_test_dummy_encryption.

> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  fs/crypto/policy.c      | 20 ++++++--------------
>  fs/ext4/super.c         |  2 +-
>  fs/f2fs/super.c         |  2 +-
>  include/linux/fscrypt.h |  5 +----
>  4 files changed, 9 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
> index 97cf07543651f..4441d9944b9ef 100644
> --- a/fs/crypto/policy.c
> +++ b/fs/crypto/policy.c
> @@ -697,8 +697,7 @@ EXPORT_SYMBOL_GPL(fscrypt_set_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.
> + * @arg: the argument to the test_dummy_encryption option.  May be NULL.
>   * @dummy_policy: the filesystem's current dummy policy (input/output, see
>   *		  below)
>   *
> @@ -712,29 +711,23 @@ EXPORT_SYMBOL_GPL(fscrypt_set_context);
>   *         -EEXIST if a different dummy policy is already set;
>   *         or another -errno value.
>   */
> -int fscrypt_set_test_dummy_encryption(struct super_block *sb,
> -				      const substring_t *arg,
> +int fscrypt_set_test_dummy_encryption(struct super_block *sb, const char *arg,
>  				      struct fscrypt_dummy_policy *dummy_policy)
>  {
> -	const char *argstr = "v2";
> -	const char *argstr_to_free = NULL;
>  	struct fscrypt_key_specifier key_spec = { 0 };
>  	int version;
>  	union fscrypt_policy *policy = NULL;
>  	int err;
>  
> -	if (arg->from) {
> -		argstr = argstr_to_free = match_strdup(arg);
> -		if (!argstr)
> -			return -ENOMEM;
> -	}
> +	if (!arg)
> +		arg = "v2";
>  
> -	if (!strcmp(argstr, "v1")) {
> +	if (!strcmp(arg, "v1")) {
>  		version = FSCRYPT_POLICY_V1;
>  		key_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
>  		memset(key_spec.u.descriptor, 0x42,
>  		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
> -	} else if (!strcmp(argstr, "v2")) {
> +	} else if (!strcmp(arg, "v2")) {
>  		version = FSCRYPT_POLICY_V2;
>  		key_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
>  		/* key_spec.u.identifier gets filled in when adding the key */
> @@ -785,7 +778,6 @@ int fscrypt_set_test_dummy_encryption(struct super_block *sb,
>  	err = 0;
>  out:
>  	kfree(policy);
> -	kfree(argstr_to_free);
>  	return err;
>  }
>  EXPORT_SYMBOL_GPL(fscrypt_set_test_dummy_encryption);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 7e77722406e2f..ed5624285a475 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1893,7 +1893,7 @@ static int ext4_set_test_dummy_encryption(struct super_block *sb,
>  			 "Can't set test_dummy_encryption on remount");
>  		return -1;
>  	}
> -	err = fscrypt_set_test_dummy_encryption(sb, arg,
> +	err = fscrypt_set_test_dummy_encryption(sb, arg->from,
>  						&sbi->s_dummy_enc_policy);
>  	if (err) {
>  		if (err == -EEXIST)
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index f2b3d1a279fb7..c72d22c0c52e7 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -438,7 +438,7 @@ static int f2fs_set_test_dummy_encryption(struct super_block *sb,
>  		return -EINVAL;
>  	}
>  	err = fscrypt_set_test_dummy_encryption(
> -		sb, arg, &F2FS_OPTION(sbi).dummy_enc_policy);
> +		sb, arg->from, &F2FS_OPTION(sbi).dummy_enc_policy);
>  	if (err) {
>  		if (err == -EEXIST)
>  			f2fs_warn(sbi,
> diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
> index b3b0c5675c6b1..fc67c4cbaa968 100644
> --- a/include/linux/fscrypt.h
> +++ b/include/linux/fscrypt.h
> @@ -15,7 +15,6 @@
>  
>  #include <linux/fs.h>
>  #include <linux/mm.h>
> -#include <linux/parser.h>
>  #include <linux/slab.h>
>  #include <uapi/linux/fscrypt.h>
>  
> @@ -153,9 +152,7 @@ struct fscrypt_dummy_policy {
>  	const union fscrypt_policy *policy;
>  };
>  
> -int fscrypt_set_test_dummy_encryption(
> -				struct super_block *sb,
> -				const substring_t *arg,
> +int fscrypt_set_test_dummy_encryption(struct super_block *sb, const char *arg,
>  				struct fscrypt_dummy_policy *dummy_policy);
>  void fscrypt_show_test_dummy_encryption(struct seq_file *seq, char sep,
>  					struct super_block *sb);

-- 
Jeff Layton <jlayton@kernel.org>