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.
> ---
> arch/x86/kernel/crash.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 9730c88530fc..0d651c05a49e 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -403,6 +403,8 @@ int crash_load_segments(struct kimage *image)
> ret = kexec_add_buffer(&kbuf);
> if (ret) {
> vfree((void *)image->elf_headers);
> + image->elf_headers = NULL;
> + image->elf_headers_sz = 0;
> return ret;
> }
> image->elf_load_addr = kbuf.mem;
