scsi: target: replace deprecated strncpy with strscpy

Commit Message

Justin Stitt March 18, 2024, 9:32 p.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.

We expect db_root and db_root_stage to be NUL-terminated based on its
immediate use with pr_debug which expects a C-string argument (%s).
Moreover, it seems NUL-padding is not required.

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Additionally, we should also change snprintf() to scnprintf().
`read_bytes` may be improperly assigned as snprintf() does NOT return
the number of bytes written into the destination buffer, rather it
returns the number of bytes that COULD have been written to that buffer
if it had ample space. Conversely, scnprintf() returns the actual number
of bytes written into the destination buffer (except the NUL-byte). This
essentially means the ``if (!read_bytes)`` was probably never a possible
branch.

After these changes, this code is more self-describing since it uses
string APIs that more accurately match the desired behavior.

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: [e-mail]
Signed-off-by: Justin Stitt <[e-mail]>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/target/target_core_configfs.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)


---
base-commit: bf3a69c6861ff4dc7892d895c87074af7bc1c400
change-id: 20240315-strncpy-drivers-target-target_core_configfs-c-fbe862bf950a

Best regards,
--
Justin Stitt <[e-mail]>

Comments

Kees Cook March 18, 2024, 9:42 p.m. UTC | #1

On Mon, Mar 18, 2024 at 09:32:01PM +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.
> 
> We expect db_root and db_root_stage to be NUL-terminated based on its
> immediate use with pr_debug which expects a C-string argument (%s).
> Moreover, it seems NUL-padding is not required.
> 
> Considering the above, a suitable replacement is `strscpy` [2] due to
> the fact that it guarantees NUL-termination on the destination buffer
> without unnecessarily NUL-padding.
> 
> Additionally, we should also change snprintf() to scnprintf().
> `read_bytes` may be improperly assigned as snprintf() does NOT return
> the number of bytes written into the destination buffer, rather it
> returns the number of bytes that COULD have been written to that buffer
> if it had ample space. Conversely, scnprintf() returns the actual number
> of bytes written into the destination buffer (except the NUL-byte). This
> essentially means the ``if (!read_bytes)`` was probably never a possible
> branch.
> 
> After these changes, this code is more self-describing since it uses
> string APIs that more accurately match the desired behavior.
> 
> 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: [e-mail]
> Signed-off-by: Justin Stitt <[e-mail]>

Good catch on "read_bytes"!

Reviewed-by: Kees Cook <[e-mail]>

Patch

diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
index c1fbcdd16182..d78647e4f6c5 100644
--- a/drivers/target/target_core_configfs.c
+++ b/drivers/target/target_core_configfs.c
@@ -123,7 +123,7 @@  static ssize_t target_core_item_dbroot_store(struct config_item *item,
 		goto unlock;
 	}
 
-	read_bytes = snprintf(db_root_stage, DB_ROOT_LEN, "%s", page);
+	read_bytes = scnprintf(db_root_stage, DB_ROOT_LEN, "%s", page);
 	if (!read_bytes)
 		goto unlock;
 
@@ -143,7 +143,7 @@  static ssize_t target_core_item_dbroot_store(struct config_item *item,
 	}
 	filp_close(fp, NULL);
 
-	strncpy(db_root, db_root_stage, read_bytes);
+	strscpy(db_root, db_root_stage, sizeof(db_root));
 	pr_debug("Target_Core_ConfigFS: db_root set to %s\n", db_root);
 
 	r = read_bytes;
@@ -3651,7 +3651,7 @@  static void target_init_dbroot(void)
 {
 	struct file *fp;
 
-	snprintf(db_root_stage, DB_ROOT_LEN, DB_ROOT_PREFERRED);
+	scnprintf(db_root_stage, DB_ROOT_LEN, DB_ROOT_PREFERRED);
 	fp = filp_open(db_root_stage, O_RDONLY, 0);
 	if (IS_ERR(fp)) {
 		pr_err("db_root: cannot open: %s\n", db_root_stage);
@@ -3664,7 +3664,7 @@  static void target_init_dbroot(void)
 	}
 	filp_close(fp, NULL);
 
-	strncpy(db_root, db_root_stage, DB_ROOT_LEN);
+	strscpy(db_root, db_root_stage, sizeof(db_root));
 	pr_debug("Target_Core_ConfigFS: db_root set to %s\n", db_root);
 }