lkml.org 
[lkml]   [2023]   [Aug]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
Subject[PATCH v2] arm64/sysreg: refactor deprecated strncpy
From
`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: 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 <keescook@chromium.org>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- Utilize return value from strscpy and check for truncation (thanks Kees)
- Link to v1: https://lore.kernel.org/r/20230810-strncpy-arch-arm64-v1-1-f67f3685cd64@google.com
---
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 <justinstitt@google.com>

\
 
 \ /
  Last update: 2023-08-11 18:34    [W:0.218 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site