Commit f700b719 authored by Justin Stitt's avatar Justin Stitt Committed by Kees Cook
Browse files

fs: ecryptfs: replace deprecated strncpy with strscpy 

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces. A good alternative is strscpy() as it guarantees
NUL-termination on the destination buffer.

In crypto.c:
We expect cipher_name to be NUL-terminated based on its use with
the C-string format specifier %s and with other string apis like
strlen():
|	printk(KERN_ERR "Error attempting to initialize key TFM "
|		"cipher with name = [%s]; rc = [%d]\n",
|		tmp_tfm->cipher_name, rc);
and
|	int cipher_name_len = strlen(cipher_name);

In main.c:
We can remove the manual NUL-byte assignments as well as the pointers to
destinations (which I assume only existed to trim down on line length?)
in favor of directly using the destination buffer which allows the
compiler to get size information -- enabling the usage of the new
2-argument strscpy().

Note that this patch relies on the _new_ 2-argument versions of
strscpy() and strscpy_pad() introduced in Commit e6584c39 ("string:
Allow 2-argument strscpy()").

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90


Cc:  <linux-hardening@vger.kernel.org>
Signed-off-by: default avatarJustin Stitt <justinstitt@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240321-strncpy-fs-ecryptfs-crypto-c-v1-1-d78b74c214ac@google.com


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 7dcbf17e

fs/ecryptfs/crypto.c

+1 −3
Original line number Diff line number Diff line
@@ -1606,9 +1606,7 @@ ecryptfs_add_new_key_tfm(struct ecryptfs_key_tfm **key_tfm, char *cipher_name, 
		goto out;

	}

	mutex_init(&tmp_tfm->key_tfm_mutex);

	strncpy(tmp_tfm->cipher_name, cipher_name,

		ECRYPTFS_MAX_CIPHER_NAME_SIZE);

	tmp_tfm->cipher_name[ECRYPTFS_MAX_CIPHER_NAME_SIZE] = '\0';

	strscpy(tmp_tfm->cipher_name, cipher_name);

	tmp_tfm->key_size = key_size;

	rc = ecryptfs_process_key_cipher(&tmp_tfm->key_tfm,

					 tmp_tfm->cipher_name,

fs/ecryptfs/main.c

+6 −20
Original line number Diff line number Diff line
@@ -256,11 +256,8 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options, 
	substring_t args[MAX_OPT_ARGS];

	int token;

	char *sig_src;

	char *cipher_name_dst;

	char *cipher_name_src;

	char *fn_cipher_name_dst;

	char *fn_cipher_name_src;

	char *fnek_dst;

	char *fnek_src;

	char *cipher_key_bytes_src;

	char *fn_cipher_key_bytes_src;
@@ -293,12 +290,8 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options, 
		case ecryptfs_opt_cipher:

		case ecryptfs_opt_ecryptfs_cipher:

			cipher_name_src = args[0].from;

			cipher_name_dst =

				mount_crypt_stat->

				global_default_cipher_name;

			strncpy(cipher_name_dst, cipher_name_src,

				ECRYPTFS_MAX_CIPHER_NAME_SIZE);

			cipher_name_dst[ECRYPTFS_MAX_CIPHER_NAME_SIZE] = '\0';

			strscpy(mount_crypt_stat->global_default_cipher_name,

				cipher_name_src);

			cipher_name_set = 1;

			break;

		case ecryptfs_opt_ecryptfs_key_bytes:
@@ -326,11 +319,8 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options, 
			break;

		case ecryptfs_opt_fnek_sig:

			fnek_src = args[0].from;

			fnek_dst =

				mount_crypt_stat->global_default_fnek_sig;

			strncpy(fnek_dst, fnek_src, ECRYPTFS_SIG_SIZE_HEX);

			mount_crypt_stat->global_default_fnek_sig[

				ECRYPTFS_SIG_SIZE_HEX] = '\0';

			strscpy(mount_crypt_stat->global_default_fnek_sig,

				fnek_src);

			rc = ecryptfs_add_global_auth_tok(

				mount_crypt_stat,

				mount_crypt_stat->global_default_fnek_sig,
@@ -348,12 +338,8 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options, 
			break;

		case ecryptfs_opt_fn_cipher:

			fn_cipher_name_src = args[0].from;

			fn_cipher_name_dst =

				mount_crypt_stat->global_default_fn_cipher_name;

			strncpy(fn_cipher_name_dst, fn_cipher_name_src,

				ECRYPTFS_MAX_CIPHER_NAME_SIZE);

			mount_crypt_stat->global_default_fn_cipher_name[

				ECRYPTFS_MAX_CIPHER_NAME_SIZE] = '\0';

			strscpy(mount_crypt_stat->global_default_fn_cipher_name,

				fn_cipher_name_src);

			fn_cipher_name_set = 1;

			break;

		case ecryptfs_opt_fn_cipher_key_bytes: