Re: [PATCH v4 3/9] crash_dump: Read the number of dm-crypt keys from reserved memory

[Coiby Xu <coiby.xu@gmail.com>]

On Sun, Aug 30, 2026 at 12:49:42PM +0530, Sourabh Jain wrote:
>
>
>On 28/08/26 14:18, Coiby Xu wrote:
>>In case user adds/deletes the keys by mistake, it's safer to read the
>>number of keys from reserved memory.
>>
>>Fixes: 9ebfa8dcaea7 ("crash_dump: reuse saved dm crypt keys for CPU/memory hot-plugging")
>>Reported-and-Suggested-by: Sourabh Jain <sourabhjain@linux.ibm.com>
>>Signed-off-by: Coiby Xu <coiby.xu@gmail.com>
>>---
>>  kernel/crash_dump_dm_crypt.c | 36 +++++++++++++++++++++++-------------
>>  1 file changed, 23 insertions(+), 13 deletions(-)
>>
>>diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
>>index 026c7de4ad85..0b9e09c60745 100644
>>--- a/kernel/crash_dump_dm_crypt.c
>>+++ b/kernel/crash_dump_dm_crypt.c
>>@@ -89,21 +89,31 @@ static int get_keys_from_kdump_reserved_memory(void)
>>  {
>>  	struct keys_header *keys_header_loaded;
>>  	size_t keys_header_size;
>>-
>>-	keys_header_size = get_keys_header_size(key_count);
>>-	keys_header = kzalloc(keys_header_size, GFP_KERNEL);
>>-	if (!keys_header)
>>-		return -ENOMEM;
>>+	int r = 0;
>>  	arch_kexec_unprotect_crashkres();
>>  	keys_header_loaded = kmap_local_page(pfn_to_page(
>>  		kexec_crash_image->dm_crypt_keys_addr >> PAGE_SHIFT));
>>+	if (keys_header_loaded->total_keys <= 0 ||
>>+	    keys_header_loaded->total_keys > KEY_NUM_MAX) {
>>+		pr_warn("keys_header saved to reserved memory may be corrupt\n");
>>+		r = -EINVAL;
>>+		goto kunmap;
>>+	}
>>+
>>+	keys_header_size = get_keys_header_size(keys_header_loaded->total_keys);
>>+	keys_header = kzalloc(keys_header_size, GFP_KERNEL);
>>+	if (!keys_header) {
>>+		r = -ENOMEM;
>>+		goto kunmap;
>>+	}
>>+
>>  	memcpy(keys_header, keys_header_loaded, keys_header_size);
>>+kunmap:
>>  	kunmap_local(keys_header_loaded);
>>  	arch_kexec_protect_crashkres();
>>-
>>-	return 0;
>>+	return r;
>>  }
>>  static int restore_dm_crypt_keys_to_thread_keyring(void)
>>@@ -447,12 +457,12 @@ int crash_load_dm_crypt_keys(struct kimage *image)
>>  	mutex_lock(&config_keys_subsys.su_mutex);
>>  	mutex_acquired = true;
>>-	if (key_count <= 0) {
>>-		kexec_dprintk("No dm-crypt keys\n");
>>-		return 0;
>>-	}
>>-
>>  	if (!is_dm_key_reused) {
>>+		if (key_count <= 0) {
>>+			kexec_dprintk("No dm-crypt keys\n");
>>+			return 0;
>>+		}
>>+
>
>Not directly related to this patch, but I have a query.
>
>Do we really need to take config_keys_subsys.su_mutex when keys are
>reused? If not, how about moving the acquisition and release of
>config_keys_subsys.su_mutex into build_keys_header()?

Good suggestion! I'll try to apply it to next version.

>
>
>- Sourabh Jain
>>  		r = build_keys_header();
>>  		if (r)
>>  			goto out;
>>@@ -463,7 +473,7 @@ int crash_load_dm_crypt_keys(struct kimage *image)
>>  	 * cleaned up at the end of kexec_file_load syscall
>>  	 */
>>  	kbuf.buffer = keys_header;
>>-	kbuf.bufsz = get_keys_header_size(key_count);
>>+	kbuf.bufsz = get_keys_header_size(keys_header->total_keys);
>>  	kbuf.memsz = kbuf.bufsz;
>>  	kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
>

-- 
Best regards,
Coiby