[PATCH] reiserfs: replace deprecated strncpy with scnprintf

[PATCH] reiserfs: replace deprecated strncpy with scnprintf

[Justin Stitt]

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

Our goal here is to get @namebuf populated with @name's contents but
surrounded with quotes. There is some careful handling done to ensure we
properly truncate @name so that we have room for a literal quote as well
as a NUL-term. All this careful handling can be done with scnprintf
using the dynamic string width specifier %.*s which allows us to pass in
the max size for a source string. Doing this, we can put literal quotes
in our format specifier and ensure @name is truncated to fit inbetween
these quotes (-3 is from 2 quotes + 1 NUL-byte).

All in all, we get to remove a deprecated use of strncpy and clean up
this code nicely!

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>
---
I realize this file has been marked as "obsolete" as told by checkpatch:
|	WARNING: fs/reiserfs/item_ops.c is marked as 'obsolete' in the MAINTAINERS hierarchy.  No unnecessary modifications please.

... but I really want to remove ALL instances of strncpy so we can rip
it out of the kernel as per: https://github.com/KSPP/linux/issues/90.
---
 fs/reiserfs/item_ops.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/fs/reiserfs/item_ops.c b/fs/reiserfs/item_ops.c
index 3a5a752d96c7..5011c10287c6 100644
--- a/fs/reiserfs/item_ops.c
+++ b/fs/reiserfs/item_ops.c
@@ -389,16 +389,9 @@ static void direntry_print_item(struct item_head *ih, char *item)
 		name = item + deh_location(deh);
 		if (name[namelen - 1] == 0)
 			namelen = strlen(name);
-		namebuf[0] = '"';
-		if (namelen > sizeof(namebuf) - 3) {
-			strncpy(namebuf + 1, name, sizeof(namebuf) - 3);
-			namebuf[sizeof(namebuf) - 2] = '"';
-			namebuf[sizeof(namebuf) - 1] = 0;
-		} else {
-			memcpy(namebuf + 1, name, namelen);
-			namebuf[namelen + 1] = '"';
-			namebuf[namelen + 2] = 0;
-		}
+
+		scnprintf(namebuf, sizeof(namebuf), "\"%.*s\"",
+			  (int)sizeof(namebuf)-3, name);
 
 		printk("%d:  %-15s%-15d%-15d%-15lld%-15lld(%s)\n",
 		       i, namebuf,

---
base-commit: 928a87efa42302a23bb9554be081a28058495f22
change-id: 20240328-strncpy-fs-reiserfs-item_ops-c-c2f9b8a6c1f3

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

Re: [PATCH] reiserfs: replace deprecated strncpy with scnprintf

[Kees Cook]

On Thu, Mar 28, 2024 at 09:16:52PM +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.
> 
> Our goal here is to get @namebuf populated with @name's contents but
> surrounded with quotes. There is some careful handling done to ensure we
> properly truncate @name so that we have room for a literal quote as well
> as a NUL-term. All this careful handling can be done with scnprintf
> using the dynamic string width specifier %.*s which allows us to pass in
> the max size for a source string. Doing this, we can put literal quotes
> in our format specifier and ensure @name is truncated to fit inbetween
> these quotes (-3 is from 2 quotes + 1 NUL-byte).
> 
> All in all, we get to remove a deprecated use of strncpy and clean up
> this code nicely!
> 
> 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>

Yeah, I like the use of %.*s here. This is much more clear now I think.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH] reiserfs: replace deprecated strncpy with scnprintf

[Kees Cook]

On Thu, 28 Mar 2024 21:16:52 +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.
> 
> Our goal here is to get @namebuf populated with @name's contents but
> surrounded with quotes. There is some careful handling done to ensure we
> properly truncate @name so that we have room for a literal quote as well
> as a NUL-term. All this careful handling can be done with scnprintf
> using the dynamic string width specifier %.*s which allows us to pass in
> the max size for a source string. Doing this, we can put literal quotes
> in our format specifier and ensure @name is truncated to fit inbetween
> these quotes (-3 is from 2 quotes + 1 NUL-byte).
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] reiserfs: replace deprecated strncpy with scnprintf
      https://git.kernel.org/kees/c/ba287092ae90

Take care,

-- 
Kees Cook