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Message-ID: <20230811-strncpy-arch-arm64-v2-1-ba84eabffadb@google.com>
Date: Fri, 11 Aug 2023 16:33:51 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Kees Cook <keescook@...omium.org>,
linux-hardening@...r.kernel.org,
Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH v2] arm64/sysreg: refactor deprecated strncpy
`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@...omium.org>
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.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@...gle.com>
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