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

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

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;
+		}
+
 		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;
-- 
2.55.0