[PATCH v3 07/17] crash_dump: Fix potential double-free of keys_header

`keys_header` was freed in `build_keys_header()` without being reset
to NULL, and the error path in `crash_load_dm_crypt_keys()` freed it
unconditionally even when reused, leading to double-free or
use-after-free.

Add `free_keys_header()` to centralize freeing and NULL-setting.
Use it in `build_keys_header()` and only free in the error path when
the header was newly built (`!is_dm_key_reused`).

Cc: Andrew Morton <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Dave Young <[email protected]>
Cc: [email protected]
Fixes: e3a84be1ec2f ("arm64,ppc64le/kdump: pass dm-crypt keys to kdump kernel")
Signed-off-by: Jinjie Ruan <[email protected]>
---
 kernel/crash_dump_dm_crypt.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
index c685497cd470..ed0960ff0987 100644
--- a/kernel/crash_dump_dm_crypt.c
+++ b/kernel/crash_dump_dm_crypt.c
@@ -363,15 +363,21 @@ static struct configfs_subsystem config_keys_subsys = {
 	},
 };
 
+static void free_keys_header(void)
+{
+	if (keys_header) {
+		kvfree(keys_header);
+		keys_header = NULL;
+	}
+}
+
 static int build_keys_header(void)
 {
 	struct config_item *item = NULL;
 	struct config_key *key;
 	int i, r;
 
-	if (keys_header != NULL)
-		kvfree(keys_header);
-
+	free_keys_header();
 	keys_header = kzalloc(get_keys_header_size(key_count), GFP_KERNEL);
 	if (!keys_header)
 		return -ENOMEM;
@@ -441,7 +447,8 @@ int crash_load_dm_crypt_keys(struct kimage *image)
 	r = kexec_add_buffer(&kbuf);
 	if (r) {
 		pr_err("Failed to call kexec_add_buffer, ret=%d\n", r);
-		kvfree((void *)kbuf.buffer);
+		if (!is_dm_key_reused)
+			free_keys_header();
 		return r;
 	}
 	image->dm_crypt_keys_addr = kbuf.mem;
-- 
2.34.1