From ada2e5a44e99113e08ad9b7b71396c6c572204da Mon Sep 17 00:00:00 2001 From: Guangshuo Li Date: Sat, 4 Jul 2026 19:25:09 +0800 Subject: [PATCH] crash_dump: release keyring reference at the correct time restore_dm_crypt_keys_to_thread_keyring() gets a reference to the user keyring before restoring the saved dm-crypt keys. The same keyring reference is then passed to add_key_to_keyring() for each saved key, but add_key_to_keyring() drops that reference on every call. This is only balanced when exactly one key is restored. With multiple keys, the keyring reference is dropped too many times and may trigger a refcount underflow or use-after-free. When more than five keys are restored, a refcount underflow/use-after-free warning can be triggered. The early error paths after lookup_user_key() also return without dropping the keyring reference. Keep ownership of the keyring reference in restore_dm_crypt_keys_to_thread_keyring(), drop it once on all exit paths, and make add_key_to_keyring() only use the reference without consuming it. Fixes: 62f17d9df692 ("crash_dump: retrieve dm crypt keys in kdump kernel") Signed-off-by: Guangshuo Li Reviewed-and-tested-by: Coiby Xu Acked-by: Baoquan He Reviewed-by: Bradley Morgan Link: https://patch.msgid.link/20260704112509.3717884-1-lgs201920130244@gmail.com Signed-off-by: Mike Rapoport (Microsoft) --- kernel/crash_dump_dm_crypt.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c index cb875ddb6ba6..c685497cd470 100644 --- a/kernel/crash_dump_dm_crypt.c +++ b/kernel/crash_dump_dm_crypt.c @@ -81,7 +81,6 @@ static int add_key_to_keyring(struct dm_crypt_key *dm_key, kexec_dprintk("Error when adding key"); } - key_ref_put(keyring_ref); return r; } @@ -104,6 +103,7 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) struct dm_crypt_key *key; size_t keys_header_size; key_ref_t keyring_ref; + int ret = 0; u64 addr; /* find the target keyring (which must be writable) */ @@ -118,7 +118,8 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) dm_crypt_keys_read((char *)&key_count, sizeof(key_count), &addr); if (key_count > KEY_NUM_MAX) { kexec_dprintk("Failed to read the number of dm-crypt keys\n"); - return -1; + ret = -1; + goto out; } kexec_dprintk("There are %u keys\n", key_count); @@ -126,8 +127,10 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) keys_header_size = get_keys_header_size(key_count); keys_header = kzalloc(keys_header_size, GFP_KERNEL); - if (!keys_header) - return -ENOMEM; + if (!keys_header) { + ret = -ENOMEM; + goto out; + } dm_crypt_keys_read((char *)keys_header, keys_header_size, &addr); @@ -137,7 +140,9 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) add_key_to_keyring(key, keyring_ref); } - return 0; +out: + key_ref_put(keyring_ref); + return ret; } static int read_key_from_user_keyring(struct dm_crypt_key *dm_key)