[RFC v2 2/5] crash_dump: save the LUKS volume key temporarily

[Coiby Xu]

After having the volume key, crytpsetup/systemd-cryptsetup saves the
volume key as a logon key to its thread keyring and this key is
destroyed immediately with the terminated thread. So a temporary copy of
the volume key is needed in order to later save it to kdump reserved
memory when the crash kernel is loaded later.

crytpsetup/systemd-cryptsetup will write the key description to
/sys/kernel/crash_luks_volume_key so the kernel will read the logon key
and save a temporary copy for later user. kdump has 1 hour at maximum to
get the temporary copy before the key gets wiped. And after kdump
retrieves the key, the key will be wiped immediately.

Signed-off-by: Coiby Xu <coxu@xxxxxxxxxx>
---
 include/linux/crash_core.h |  2 +
 kernel/crash_dump.c        | 88 ++++++++++++++++++++++++++++++++++++++
 kernel/ksysfs.c            | 19 ++++++++
 3 files changed, 109 insertions(+)

diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index de62a722431e..596d83b8f362 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -83,5 +83,7 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
 		unsigned long long *crash_size, unsigned long long *crash_base);
 int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
 		unsigned long long *crash_size, unsigned long long *crash_base);
+int crash_sysfs_luks_volume_key_write(const char *key_des, size_t count);
+int crash_pass_temp_luks_volume_key(void **addr, unsigned long *sz);
 
 #endif /* LINUX_CRASH_CORE_H */
diff --git a/kernel/crash_dump.c b/kernel/crash_dump.c
index 92da32275af5..9c202bffbb8d 100644
--- a/kernel/crash_dump.c
+++ b/kernel/crash_dump.c
@@ -5,6 +5,7 @@
 #include <linux/errno.h>
 #include <linux/export.h>
 
+#include <keys/user-type.h>
 /*
  * stores the physical address of elf header of crash image
  *
@@ -39,3 +40,90 @@ static int __init setup_elfcorehdr(char *arg)
 	return end > arg ? 0 : -EINVAL;
 }
 early_param("elfcorehdr", setup_elfcorehdr);
+
+static u8 *luks_volume_key;
+static unsigned int luks_volume_key_size;
+
+void wipe_luks_volume_key(void)
+{
+	if (luks_volume_key) {
+		memset(luks_volume_key, 0, luks_volume_key_size * sizeof(u8));
+		kfree(luks_volume_key);
+		luks_volume_key = NULL;
+	}
+}
+
+static void _wipe_luks_volume_key(struct work_struct *dummy)
+{
+	wipe_luks_volume_key();
+}
+
+static DECLARE_DELAYED_WORK(wipe_luks_volume_key_work, _wipe_luks_volume_key);
+
+static unsigned __read_mostly wipe_key_delay = 3600; /* 1 hour */
+
+static int crash_save_temp_luks_volume_key(const char *key_desc, size_t count)
+{
+	const struct user_key_payload *ukp;
+	struct key *key;
+
+
+	if (luks_volume_key) {
+		memset(luks_volume_key, 0, luks_volume_key_size * sizeof(u8));
+		kfree(luks_volume_key);
+	}
+
+	pr_debug("Requesting key %s", key_desc);
+	key = request_key(&key_type_logon, key_desc, NULL);
+
+	if (IS_ERR(key)) {
+		pr_debug("No such key %s", key_desc);
+		return PTR_ERR(key);
+	}
+
+	ukp = user_key_payload_locked(key);
+	if (!ukp)
+		return -EKEYREVOKED;
+
+	luks_volume_key = kmalloc(ukp->datalen, GFP_KERNEL);
+	if (!luks_volume_key)
+		return -ENOMEM;
+	memcpy(luks_volume_key, ukp->data, ukp->datalen);
+	luks_volume_key_size = ukp->datalen;
+	pr_debug("LUKS master key (size=%u): %8ph\n", luks_volume_key_size, luks_volume_key);
+	schedule_delayed_work(&wipe_luks_volume_key_work,
+			      round_jiffies_relative(wipe_key_delay * HZ));
+	return 0;
+}
+
+int crash_sysfs_luks_volume_key_write(const char *key_desc, size_t count)
+{
+	if (!is_kdump_kernel())
+		return crash_save_temp_luks_volume_key(key_desc, count);
+	return -EINVAL;
+}
+EXPORT_SYMBOL(crash_sysfs_luks_volume_key_write);
+
+int crash_pass_temp_luks_volume_key(void **addr, unsigned long *sz)
+{
+	unsigned long luks_key_sz;
+	unsigned char *buf;
+	unsigned int *size_ptr;
+
+	if (!luks_volume_key)
+		return -EINVAL;
+
+	luks_key_sz = sizeof(unsigned int) + luks_volume_key_size * sizeof(u8);
+
+	buf = vzalloc(luks_key_sz);
+	if (!buf)
+		return -ENOMEM;
+
+	size_ptr = (unsigned int *)buf;
+	memcpy(size_ptr, &luks_volume_key_size, sizeof(unsigned int));
+	memcpy(size_ptr + 1, luks_volume_key, luks_volume_key_size * sizeof(u8));
+	*addr = buf;
+	*sz = luks_key_sz;
+	wipe_luks_volume_key();
+	return 0;
+}
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index b1292a57c2a5..e7a7433cb951 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -135,6 +135,24 @@ static ssize_t vmcoreinfo_show(struct kobject *kobj,
 }
 KERNEL_ATTR_RO(vmcoreinfo);
 
+static ssize_t crash_luks_volume_key_show(struct kobject *kobj,
+					  struct kobj_attribute *attr,
+					  char *buf)
+{
+	return 0;
+}
+
+static ssize_t crash_luks_volume_key_store(struct kobject *kobj,
+					   struct kobj_attribute *attr,
+					   const char *buf, size_t count)
+{
+	int ret;
+
+	ret = crash_sysfs_luks_volume_key_write(buf, count);
+	return ret < 0 ? ret : count;
+}
+KERNEL_ATTR_RW(crash_luks_volume_key);
+
 #endif /* CONFIG_CRASH_CORE */
 
 /* whether file capabilities are enabled */
@@ -223,6 +241,7 @@ static struct attribute * kernel_attrs[] = {
 #endif
 #ifdef CONFIG_CRASH_CORE
 	&vmcoreinfo_attr.attr,
+	&crash_luks_volume_key_attr.attr,
 #endif
 #ifndef CONFIG_TINY_RCU
 	&rcu_expedited_attr.attr,
-- 
2.37.3