diff mbox series

fs: ecryptfs: replace deprecated strncpy with strscpy

Message ID 20240321-strncpy-fs-ecryptfs-crypto-c-v1-1-d78b74c214ac@google.com (mailing list archive)
State Mainlined
Commit f700b71927017ca5697e8a24fd2ad5d3e06489d6
Headers show
Series fs: ecryptfs: replace deprecated strncpy with strscpy | expand

Commit Message

Justin Stitt March 21, 2024, 12:38 a.m. UTC 
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 e6584c3964f2f ("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: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 fs/ecryptfs/crypto.c |  4 +---
 fs/ecryptfs/main.c   | 26 ++++++--------------------
 2 files changed, 7 insertions(+), 23 deletions(-)


---
base-commit: a4145ce1e7bc247fd6f2846e8699473448717b37
change-id: 20240321-strncpy-fs-ecryptfs-crypto-c-a59b3cf0a3cc

Best regards,
--
Justin Stitt <justinstitt@google.com>

Comments

Kees Cook March 29, 2024, 4:08 a.m. UTC | #1 
On Thu, Mar 21, 2024 at 12:38:54AM +0000, Justin Stitt wrote:
> 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 e6584c3964f2f ("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: Justin Stitt <justinstitt@google.com>

Looks correct. I don't see any need for padding.

Reviewed-by: Kees Cook <keescook@chromium.org>
Kees Cook April 24, 2024, 11:57 p.m. UTC | #2 
On Thu, 21 Mar 2024 00:38:54 +0000, Justin Stitt wrote:
> 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);
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] fs: ecryptfs: replace deprecated strncpy with strscpy
      https://git.kernel.org/kees/c/9a2780409552

Take care,
diff mbox series

Patch

diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index 2fe0f3af1a08..d39a1a69fecc 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -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,
diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index 2dc927ba067f..577c56302314 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -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: