linux-kernel - Re: [PATCH] x86/kexec: Fix double-free of elf header buffer

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Message-ID: <Y33lkRP23X3tN1Px@MiWiFi-R3L-srv>
Date:   Wed, 23 Nov 2022 17:19:13 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Takashi Iwai <tiwai@...e.de>, kexec@...ts.infradead.org
Cc:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/kexec: Fix double-free of elf header buffer

CC kexec@...ts.infradead.org

On 11/22/22 at 12:51pm, Takashi Iwai wrote:
> The recent fix for memory leaks forgot to clear the error path that
> already does vfree() for the elf headers.  This may result in a
> double-free.

Good catch. 

The log can be improved to make the issue more obvious. How about this:
======
With commit b3e34a47f989 ("x86/kexec: fix memory leak of elf header
buffer"), freeing up image->elf_headers in error path of
crash_load_segments() is not needed, because later
kimage_file_post_load_cleanup() will cover it. And not clearing it could 
result in a double-free.

Drop the superfluous vfree() call at the error path of
crash_load_segments().
========

Other than the log part, LGTM. Thanks.

Acked-by: Baoquan He <bhe@...hat.com>

> 
> Drop the superfluous vfree() call at the error path of
> crash_load_segments().
> 
> Fixes: b3e34a47f989 ("x86/kexec: fix memory leak of elf header buffer")
> Signed-off-by: Takashi Iwai <tiwai@...e.de>
> ---
>  arch/x86/kernel/crash.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 9730c88530fc..305514431f26 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -401,10 +401,8 @@ int crash_load_segments(struct kimage *image)
>  	kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
>  	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>  	ret = kexec_add_buffer(&kbuf);
> -	if (ret) {
> -		vfree((void *)image->elf_headers);
> +	if (ret)
>  		return ret;
> -	}
>  	image->elf_load_addr = kbuf.mem;
>  	pr_debug("Loaded ELF headers at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
>  		 image->elf_load_addr, kbuf.bufsz, kbuf.memsz);
> -- 
> 2.35.3
>