efi-pstore: Fix write/erase id tracking

Prior to the pstore interface refactoring, the "id" generated during
a backend pstore_write() was only retained by the internal pstore
inode tracking list. Additionally the "part" was ignored, so EFI
would encode this in the id. This corrects the misunderstandings
and correctly sets "id" during pstore_write(), and uses "part"
directly during pstore_erase().
Reported-by: Marta Lofstedt <marta.lofstedt@intel.com>
Fixes: 76cc9580 ("pstore: Replace arguments for write() API")
Fixes: a61072aa ("pstore: Replace arguments for erase() API")
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Marta Lofstedt <marta.lofstedt@intel.com>

drivers/firmware/efi/efi-pstore.c

@@ -53,6 +53,7 @@ static int efi_pstore_read_func(struct efivar_entry *entry,
 	if (sscanf(name, "dump-type%u-%u-%d-%lu-%c",
 		   &record->type, &part, &cnt, &time, &data_type) == 5) {
 		record->id = generic_id(time, part, cnt);
+		record->part = part;
 		record->count = cnt;
 		record->time.tv_sec = time;
 		record->time.tv_nsec = 0;
@@ -64,6 +65,7 @@ static int efi_pstore_read_func(struct efivar_entry *entry,
 	} else if (sscanf(name, "dump-type%u-%u-%d-%lu",
 		   &record->type, &part, &cnt, &time) == 4) {
 		record->id = generic_id(time, part, cnt);
+		record->part = part;
 		record->count = cnt;
 		record->time.tv_sec = time;
 		record->time.tv_nsec = 0;
@@ -77,6 +79,7 @@ static int efi_pstore_read_func(struct efivar_entry *entry,
 		 * multiple logs, remains.
 		 */
 		record->id = generic_id(time, part, 0);
+		record->part = part;
 		record->count = 0;
 		record->time.tv_sec = time;
 		record->time.tv_nsec = 0;
@@ -241,9 +244,15 @@ static int efi_pstore_write(struct pstore_record *record)
 	efi_guid_t vendor = LINUX_EFI_CRASH_GUID;
 	int i, ret = 0;
 
+	record->time.tv_sec = get_seconds();
+	record->time.tv_nsec = 0;
+
+	record->id = generic_id(record->time.tv_sec, record->part,
+				record->count);
+
 	snprintf(name, sizeof(name), "dump-type%u-%u-%d-%lu-%c",
 		 record->type, record->part, record->count,
-		 get_seconds(), record->compressed ? 'C' : 'D');
+		 record->time.tv_sec, record->compressed ? 'C' : 'D');
 
 	for (i = 0; i < DUMP_NAME_LEN; i++)
 		efi_name[i] = name[i];
@@ -255,7 +264,6 @@ static int efi_pstore_write(struct pstore_record *record)
 	if (record->reason == KMSG_DUMP_OOPS)
 		efivar_run_worker();
 
-	record->id = record->part;
 	return ret;
 };
 
@@ -287,7 +295,7 @@ static int efi_pstore_erase_func(struct efivar_entry *entry, void *data)
 		 * holding multiple logs, remains.
 		 */
 		snprintf(name_old, sizeof(name_old), "dump-type%u-%u-%lu",
-			ed->record->type, (unsigned int)ed->record->id,
+			ed->record->type, ed->record->part,
 			ed->record->time.tv_sec);
 
 		for (i = 0; i < DUMP_NAME_LEN; i++)
@@ -320,10 +328,7 @@ static int efi_pstore_erase(struct pstore_record *record)
 	char name[DUMP_NAME_LEN];
 	efi_char16_t efi_name[DUMP_NAME_LEN];
 	int found, i;
-	unsigned int part;
 
-	do_div(record->id, 1000);
-	part = do_div(record->id, 100);
 	snprintf(name, sizeof(name), "dump-type%u-%u-%d-%lu",
 		 record->type, record->part, record->count,
 		 record->time.tv_sec);