Re: [PATCH] x86/kexec: fix double vfree of image->elf_headers

[Ingo Molnar]

* Vlastimil Babka <vbabka@xxxxxxx> 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@xxxxxxx>
> > Cc: Baoquan He <bhe@xxxxxxxxxx>
> > Cc: Dave Young <dyoung@xxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> 
> Takashi told me he sent a slightly different fix already in November:
> https://lore.kernel.org/all/20221122115122.13937-1-tiwai@xxxxxxx/
> 
> 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