linux-kernel - Re: [PATCH] x86/kexec: fix double vfree of image->elf

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Message-ID: <Y7QAMIu6j6Y6m8vV@gmail.com>
Date:   Tue, 3 Jan 2023 11:15:12 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Takashi Iwai <tiwai@...e.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, patches@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] x86/kexec: fix double vfree of image->elf_headers


* Vlastimil Babka <vbabka@...e.cz> wrote:

> On 1/2/23 11:39, Vlastimil Babka wrote:
> > An investigation of a "Trying to vfree() nonexistent vm area" bug
> > occurring in arch_kimage_file_post_load_cleanup() doing a
> > vfree(image->elf_headers) in our 5.14-based kernel yielded the following
> > double vfree() scenario, also present in mainline:
> > 
> > SYSCALL_DEFINE5(kexec_file_load)
> >   kimage_file_alloc_init()
> >     kimage_file_prepare_segments()
> >       arch_kexec_kernel_image_probe()
> >         kexec_image_load_default()
> >           kexec_bzImage64_ops.load()
> >             bzImage64_load()
> >               crash_load_segments()
> >                 prepare_elf_headers(image, &kbuf.buffer, &kbuf.bufsz);
> >                 image->elf_headers = kbuf.buffer;
> > 		ret = kexec_add_buffer(&kbuf);
> > 		if (ret) vfree((void *)image->elf_headers); // first vfree()
> >       if (ret) kimage_file_post_load_cleanup()
> >         vfree(image->elf_headers);                          // second vfree()
> > 
> > AFAICS the scenario is possible since v5.19 commit b3e34a47f989
> > ("x86/kexec: fix memory leak of elf header buffer") that was marked for
> > stable and also was backported to our kernel.
> > 
> > Fix the problem by setting the pointer to NULL after the first vfree().
> > Also set elf_headers_sz to 0, as kimage_file_post_load_cleanup() does.
> > 
> > Fixes: b3e34a47f989 ("x86/kexec: fix memory leak of elf header buffer")
> > Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> > Cc: Baoquan He <bhe@...hat.com>
> > Cc: Dave Young <dyoung@...hat.com>
> > Cc: <stable@...r.kernel.org>
> 
> Takashi told me he sent a slightly different fix already in November:
> https://lore.kernel.org/all/20221122115122.13937-1-tiwai@suse.de/
> 
> Seems it wasn't picked up? You might pick his then, as Baoquan acked it, and
> it's removing code, not adding it.

Thanks, indeed we missed that fix - Boris picked up that version in 
tip:x86/urgent, via:

   d00dd2f2645d ("x86/kexec: Fix double-free of elf header buffer")

	Ingo