Subject: Re: [PATCH v13 04/15] arm64: kexec_file: Fix potential buffer overflow in prepare_elf_headers()

From: Breno Leitao <[email-masked]>
Date: Mon, 11 May 2026 02:46:43 -0700

On Mon, May 11, 2026 at 11:04:43AM +0800, Jinjie Ruan wrote:
> There is a race condition between the kexec_load() system call
> (crash kernel loading path) and memory hotplug operations that can
> lead to buffer overflow and potential kernel crash.
> 
> During prepare_elf_headers(), the following steps occur:
> 1. The first for_each_mem_range() queries current System RAM memory ranges
> 2. Allocates buffer based on queried count
> 3. The 2st for_each_mem_range() populates ranges from memblock
> 
> If memory hotplug occurs between step 1 and step 3, the number of ranges
> can increase, causing out-of-bounds write when populating cmem->ranges[].
> 
> This happens because kexec_load() uses kexec_trylock (atomic_t) while
> memory hotplug uses device_hotplug_lock (mutex), so they don't serialize
> with each other.
> 
> Add the explicit bounds checking to prevent out-of-bounds access.

It seems you have a TOCTOU type of issue, and this seems to be shrinking
the window, but not fully solving it?

> Cc: Catalin Marinas <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> Cc: Andrew Morton <[email-masked]>
> Cc: Baoquan He <[email-masked]>
> Cc: Breno Leitao <[email-masked]>
> Cc: [email-masked]
> Fixes: 3751e728cef2 ("arm64: kexec_file: add crash dump support")
> Closes: https://sashiko.dev/#/patchset/20260323072745.2481719-1-ruanjinjie%40huawei.com
> Signed-off-by: Jinjie Ruan <[email-masked]>
> ---
>  arch/arm64/kernel/machine_kexec_file.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index e31fabed378a..a67e7b1abbab 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -59,6 +59,11 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
>  	cmem->max_nr_ranges = nr_ranges;
>  	cmem->nr_ranges = 0;
>  	for_each_mem_range(i, &start, &end) {
> +		if (cmem->nr_ranges >= cmem->max_nr_ranges) {
> +			ret = -ENOMEM;

-ENOMEM seems to be the the wrong errno. This isn't an allocation
failure; it's a transient race. -EBUSY or -EAGAIN would be more honest