`strncpy` is deprecated for use on NUL-terminated destination strings
[1]. Which seems to be the case here due to the forceful setting of `buf`'s
tail to 0.
A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on its destination buffer argument which is
_not_ the case for `strncpy`!
In this case, we can simplify the logic and also check for any silent
truncation by using `strscpy`'s return value.
This should have no functional change and yet uses a more robust and
less ambiguous interface whilst reducing code complexity.
Link: http://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
Suggested-by: Kees Cook <[email protected]>
Cc: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
Changes in v2:
- Utilize return value from strscpy and check for truncation (thanks Kees)
- Link to v1: https://lore.kernel.org/r/[email protected]
---
For reference, see a part of `strscpy`'s implementation here:
| /* Hit buffer length without finding a NUL; force NUL-termination. */
| if (res)
| dest[res-1] = '\0';
Note: compile tested
---
arch/arm64/kernel/idreg-override.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index 2fe2491b692c..aee12c75b738 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -262,9 +262,9 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
if (!len)
return;
- len = min(len, ARRAY_SIZE(buf) - 1);
- strncpy(buf, cmdline, len);
- buf[len] = 0;
+ len = strscpy(buf, cmdline, ARRAY_SIZE(buf));
+ if (len == -E2BIG)
+ len = ARRAY_SIZE(buf) - 1;
if (strcmp(buf, "--") == 0)
return;
---
base-commit: 52a93d39b17dc7eb98b6aa3edb93943248e03b2f
change-id: 20230810-strncpy-arch-arm64-1f3d328bd9b8
Best regards,
--
Justin Stitt <[email protected]>
On Fri, 11 Aug 2023 16:33:51 +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1]. Which seems to be the case here due to the forceful setting of `buf`'s
> tail to 0.
>
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on its destination buffer argument which is
> _not_ the case for `strncpy`!
>
> [...]
Applied to arm64 (for-next/misc), thanks!
[1/1] arm64/sysreg: refactor deprecated strncpy
https://git.kernel.org/arm64/c/d232606773a0
Cheers,
--
Will
https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev
On Thu, Sep 07, 2023 at 02:28:05PM -0700, Bjorn Andersson wrote:
> On Fri, Aug 11, 2023 at 04:33:51PM +0000, Justin Stitt wrote:
> > `strncpy` is deprecated for use on NUL-terminated destination strings
> > [1]. Which seems to be the case here due to the forceful setting of `buf`'s
> > tail to 0.
> >
> > A suitable replacement is `strscpy` [2] due to the fact that it
> > guarantees NUL-termination on its destination buffer argument which is
> > _not_ the case for `strncpy`!
> >
> > In this case, we can simplify the logic and also check for any silent
> > truncation by using `strscpy`'s return value.
> >
> > This should have no functional change and yet uses a more robust and
> > less ambiguous interface whilst reducing code complexity.
> >
>
> I'm sorry, but this patch is wrong.
>
> __parse_cmdline() is supposed to match the command line against a set of
> keywords, one word at a time. The new implementation ignores the
> word-boundaries and matches the whole command line once and then breaks
> the loop, typically without having found a match. (See below)
>
> Can we please have this patch dropped, Will?
Yup, this was fixed yesterday so please take linux-next 20230908 for a
spin and let us know how you get on.
Cheers,
Will