[PATCH v2 1/2] exfat: add dir-entry set checksum validation

[Tetsuhiro Kohada <kohada.t2@gmail.com>]

Add checksum validation for dir-entry set when getting it.
exfat_calc_entry_set_chksum_with() also validates entry-type.

** This patch depends on:
  '[PATCH v3] exfat: integrates dir-entry getting and validation'

Signed-off-by: Tetsuhiro Kohada <kohada.t2@gmail.com>
---
Changes in v2
 - Add error log if checksum mismatch

 fs/exfat/dir.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index 0b42544e6340..6f9de364a919 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -565,18 +565,27 @@ int exfat_remove_entries(struct inode *inode, struct exfat_chain *p_dir,
 	return 0;
 }
 
-void exfat_update_dir_chksum_with_entry_set(struct exfat_entry_set_cache *es)
+static int exfat_calc_entry_set_chksum(struct exfat_entry_set_cache *es, u16 *chksum)
 {
-	int chksum_type = CS_DIR_ENTRY, i;
-	unsigned short chksum = 0;
 	struct exfat_dentry *ep;
+	int i;
 
-	for (i = 0; i < es->num_entries; i++) {
-		ep = exfat_get_validated_dentry(es, i, TYPE_ALL);
-		chksum = exfat_calc_chksum16(ep, DENTRY_SIZE, chksum,
-					     chksum_type);
-		chksum_type = CS_DEFAULT;
+	ep = container_of(es->de_file, struct exfat_dentry, dentry.file);
+	*chksum = exfat_calc_chksum16(ep, DENTRY_SIZE, 0, CS_DIR_ENTRY);
+	for (i = 0; i < es->de_file->num_ext; i++) {
+		ep = exfat_get_validated_dentry(es, 1 + i, TYPE_SECONDARY);
+		if (!ep)
+			return -EIO;
+		*chksum = exfat_calc_chksum16(ep, DENTRY_SIZE, *chksum, CS_DEFAULT);
 	}
+	return 0;
+}
+
+void exfat_update_dir_chksum_with_entry_set(struct exfat_entry_set_cache *es)
+{
+	u16 chksum;
+
+	exfat_calc_entry_set_chksum(es, &chksum);
 	es->de_file->checksum = cpu_to_le16(chksum);
 	es->modified = true;
 }
@@ -777,6 +786,7 @@ struct exfat_entry_set_cache *exfat_get_dentry_set(struct super_block *sb,
 	struct exfat_entry_set_cache *es;
 	struct exfat_dentry *ep;
 	struct buffer_head *bh;
+	u16 chksum;
 
 	if (p_dir->dir == DIR_DELETED) {
 		exfat_err(sb, "access to deleted dentry");
@@ -841,11 +851,13 @@ struct exfat_entry_set_cache *exfat_get_dentry_set(struct super_block *sb,
 		goto free_es;
 	es->de_stream = &ep->dentry.stream;
 
-	for (i = 2; i < es->num_entries; i++) {
-		if (!exfat_get_validated_dentry(es, i, TYPE_SECONDARY))
-			goto free_es;
+	if (max_entries == ES_ALL_ENTRIES &&
+	    ((exfat_calc_entry_set_chksum(es, &chksum) ||
+	      chksum != le16_to_cpu(es->de_file->checksum)))) {
+		exfat_err(sb, "invalid entry-set checksum (entry : 0x%08x, set-checksum : 0x%04x, checksum : 0x%04x)",
+			  entry, le16_to_cpu(es->de_file->checksum), chksum);
+		goto free_es;
 	}
-
 	return es;
 
 free_es:
-- 
2.25.1