[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <bce762af-0da7-bb5e-1580-b42803c183f6@redhat.com>
Date: Wed, 6 Sep 2023 14:16:30 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: Ingo Molnar <mingo@...nel.org>,
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,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] x86/platform/uv: refactor deprecated strcpy and
strncpy
Hi Ingo,
On 9/6/23 14:10, Ingo Molnar wrote:
>
> * 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?
The new version is a result of a review from my because IMHO:
strscpy(arg, val, strnchrnul(val, sizeof(arg)-1, '\n') - val + 1);
Is really unreadable / really hard to reason about if
this is actually correct and does not contain any
of by 1 bugs.
Note that the diff of v3 compared to the code before v2 landed is
actually smaller now and actually matches the subject of:
"refactor deprecated strcpy and strncpy"
Where as v2 actually touches more code / refactor things
which fall outside of a "one change per patch" approach.
The:
p = strchr(arg, '\n');
if (p)
*p = '\0';
was already there before v2 landed.
I also suggested to do a follow up patch to change things to:
strscpy(arg, val, sizeof(arg));
p = strchrnul(arg, '\n');
*p = '\0';
Which IMHO is much more readable then what has landed
now. But since v2 has already landed I guess the best
thing is just to stick with what we have upstream now...
Regards,
Hans
>
> 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))
>
Powered by blists - more mailing lists