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 e6584c3964f2f ("string:
Allow 2-argument strscpy()").

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Cc:  <linux-hardening@vger.kernel.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240321-strncpy-fs-ecryptfs-crypto-c-v1-1-d78b74c214ac@google.com
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index 2fe0f3af1a08ec5831d2609862e0e9a80c9b0475..d39a1a69feccdf20ca2b4c69311d499a91276f68 100644 (file)
--- 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 2dc927ba067fec4f05b5a78f08fa702457d2ef75..577c563023144a5fe5ac9d5a532134cd1cc58ed1 100644 (file)
--- 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: