linux-hardening - Re: [PATCH v3] x86/platform/uv: refactor deprecated strcpy and strncpy

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Date:   Wed, 6 Sep 2023 14:10:51 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Steve Wahl <steve.wahl@....com>, Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] x86/platform/uv: refactor deprecated strcpy and
 strncpy


* Justin Stitt <justinstitt@...gle.com> wrote:

> Both `strncpy` and `strcpy` are deprecated for use on NUL-terminated
> destination strings [1].
> 
> We can see that `arg` and `uv_nmi_action` are expected to be
> NUL-terminated strings due to their use within `strcmp()` and format
> strings respectively.
> 
> With this in mind, 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` or `strcpy`!
> 
> In this case, we can drop both the forced NUL-termination and the `... -1` from:
> |       strncpy(arg, val, ACTION_LEN - 1);
> as `strscpy` implicitly has this behavior.
> 
> 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
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

>  arch/x86/platform/uv/uv_nmi.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)

Note that this commit is already upstream:

  1e6f01f72855 ("x86/platform/uv: Refactor code using deprecated strcpy()/strncpy() interfaces to use strscpy()")

Below is the delta your v3 patch has compared to what is upstream - is it 
really necessary to open code it, instead of using strnchrnul() as your 
original patch did? Am I missing anything here?

Thanks,

	Ingo

--- a/arch/x86/platform/uv/uv_nmi.c
+++ b/arch/x86/platform/uv/uv_nmi.c
@@ -202,10 +202,13 @@ static int param_set_action(const char *val, const struct kernel_param *kp)
 {
 	int i;
 	int n = ARRAY_SIZE(valid_acts);
-	char arg[ACTION_LEN];
+	char arg[ACTION_LEN], *p;
 
 	/* (remove possible '\n') */
-	strscpy(arg, val, strnchrnul(val, sizeof(arg)-1, '\n') - val + 1);
+	strscpy(arg, val, sizeof(arg));
+	p = strchr(arg, '\n');
+	if (p)
+		*p = '\0';
 
 	for (i = 0; i < n; i++)
 		if (!strcmp(arg, valid_acts[i].action))