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: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
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(-)
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:
---
base-commit: a4145ce1e7bc247fd6f2846e8699473448717b37
change-id: 20240321-strncpy-fs-ecryptfs-crypto-c-a59b3cf0a3cc
Best regards,
--
Justin Stitt <[email protected]>
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: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>
Looks correct. I don't see any need for padding.
Reviewed-by: Kees Cook <[email protected]>
--
Kees Cook
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,
--
Kees Cook