linux-kernel - Re: [PATCH v3 1/2] x86: Add strlcat() to compressed kernel

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Date:   Thu, 12 May 2022 13:10:51 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Baskov Evgeniy <baskov@...ras.ru>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] x86: Add strlcat() to compressed kernel

On Thu, May 05, 2022 at 01:32:23PM +0300, Baskov Evgeniy wrote:
> Subject: Re: [PATCH v3 1/2] x86: Add strlcat() to compressed kernel

The tip tree preferred format for patch subject prefixes is
'subsys/component:', e.g. 'x86/apic:', 'x86/mm/fault:', 'sched/fair:',
'genirq/core:'. Please do not use file names or complete file paths as
prefix. 'git log path/to/file' should give you a reasonable hint in most
cases.

The condensed patch description in the subject line should start with a
uppercase letter and should be written in imperative tone.

In your case, that would be x86/boot: Add...

> strlcat() simplifies the code of command line
> concatenation and reduces the probability of mistakes.
> 
> Signed-off-by: Baskov Evgeniy <baskov@...ras.ru>
> 
> diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
> index 81fc1eaa3229..b0635539b6f6 100644
> --- a/arch/x86/boot/compressed/string.c
> +++ b/arch/x86/boot/compressed/string.c
> @@ -40,6 +40,21 @@ static void *____memcpy(void *dest, const void *src, size_t n)
>  }
>  #endif
>  
> +size_t strlcat(char *dest, const char *src, size_t count)
> +{
> +	size_t dsize = strlen(dest);
> +	size_t len = strlen(src);
> +	size_t res = dsize + len;

You can add the BUG_ON() check from the kernel proper version like this:

diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
index b0635539b6f6..643fcd957527 100644
--- a/arch/x86/boot/compressed/string.c
+++ b/arch/x86/boot/compressed/string.c
@@ -46,6 +46,10 @@ size_t strlcat(char *dest, const char *src, size_t count)
 	size_t len = strlen(src);
 	size_t res = dsize + len;
 
+        /* This would be a bug */
+        if (dsize >= count)
+		error("strlcat(): destination too big\n");
+
 	dest += dsize;
 	count -= dsize;
 	if (len >= count)
diff --git a/arch/x86/purgatory/purgatory.c b/arch/x86/purgatory/purgatory.c
index 7558139920f8..65f0cedb65ae 100644
--- a/arch/x86/purgatory/purgatory.c
+++ b/arch/x86/purgatory/purgatory.c
@@ -57,3 +57,4 @@ void purgatory(void)
  * arch/x86/boot/compressed/string.c
  */
 void warn(const char *msg) {}
+void error(char *m) {}

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette