linux-kernel - Re: [PATCH] x86/kaslr: Fix potential dereference of NULL pointer.

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Date:   Tue, 18 Apr 2023 15:43:33 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Daniil Dulov <d.dulov@...ddin.ru>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH] x86/kaslr: Fix potential dereference of NULL pointer.

On 04/17/23 at 11:53pm, Daniil Dulov wrote:
> Pointer val can have NULL value. Then its value is assigned to the pointer p.
> p is dereferenced by calling strcmp().
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.

It's true for strcmp from lib/string.c, while may not be so true for
strcmp in arch/x86/boot/string.c which I copy at below for reference.
Here, boot/compressed/kaslr.c is using the strcmp in
arch/x86/boot/string.c. So leaving it as is or fixing it, either looks
good to me, I even prefer the former.

int strcmp(const char *str1, const char *str2)
{
        const unsigned char *s1 = (const unsigned char *)str1;
        const unsigned char *s2 = (const unsigned char *)str2;
        int delta = 0;

        while (*s1 || *s2) {
                delta = *s1 - *s2;
                if (delta)
                        return delta;
                s1++;
                s2++;
        }
        return 0;
}

> 
> Fixes: 4cdba14f84c9 ("x86/KASLR: Handle the memory limit specified by the 'memmap=' and 'mem=' boot options")
> Signed-off-by: Daniil Dulov <d.dulov@...ddin.ru>
> ---
>  arch/x86/boot/compressed/kaslr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index b92fffbe761f..51b3925d4d2d 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -291,7 +291,7 @@ static void handle_mem_options(void)
>  		} else if (!strcmp(param, "mem")) {
>  			char *p = val;
>  
> -			if (!strcmp(p, "nopentium"))
> +			if (!p || !strcmp(p, "nopentium"))
>  				continue;
>  			mem_size = memparse(p, &p);
>  			if (mem_size == 0)
> -- 
> 2.25.1
>