linux-kernel - [PATCH v4 4/5] exfat: add dir-entry set checksum validation

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Date:   Wed, 26 Aug 2020 20:57:40 +0900
From:   Tetsuhiro Kohada <kohada.t2@...il.com>
To:     kohada.t2@...il.com
Cc:     kohada.tetsuhiro@...mitsubishielectric.co.jp,
        mori.takahiro@...mitsubishielectric.co.jp,
        motai.hirotaka@...mitsubishielectric.co.jp,
        Namjae Jeon <namjae.jeon@...sung.com>,
        Sungjong Seo <sj1557.seo@...sung.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 4/5] exfat: add dir-entry set checksum validation

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

Signed-off-by: Tetsuhiro Kohada <kohada.t2@...il.com>
---
Changes in v2
 - Add error log if checksum mismatch
Changes in v3:
 - Nothing
Changes in v4:
 - Into patch series '[PATCH v4] exfat: integrates dir-entry getting and validation'

 fs/exfat/dir.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index cd37091844fa..d4beea796708 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -565,18 +565,26 @@ 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;
-	u16 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;
+	*chksum = exfat_calc_chksum16(es->ep_file, DENTRY_SIZE, 0, CS_DIR_ENTRY);
+	for (i = 0; i < ES_FILE(es).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_FILE(es).checksum = cpu_to_le16(chksum);
 	es->modified = true;
 }
@@ -776,6 +784,7 @@ struct exfat_entry_set_cache *exfat_get_dentry_set(struct super_block *sb,
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 	struct exfat_entry_set_cache *es;
 	struct buffer_head *bh;
+	u16 chksum;
 
 	if (p_dir->dir == DIR_DELETED) {
 		exfat_err(sb, "access to deleted dentry");
@@ -839,9 +848,12 @@ struct exfat_entry_set_cache *exfat_get_dentry_set(struct super_block *sb,
 		goto free_es;
 
 	if (max_entries == ES_ALL_ENTRIES) {
-		for (i = 0; i < ES_FILE(es).num_ext; i++)
-			if (!exfat_get_validated_dentry(es, ES_INDEX_STREAM + i, TYPE_SECONDARY))
-				goto free_es;
+		if (exfat_calc_entry_set_chksum(es, &chksum) ||
+		   chksum != le16_to_cpu(ES_FILE(es).checksum)) {
+			exfat_err(sb, "invalid entry-set checksum (entry : 0x%08x, set-checksum : 0x%04x, checksum : 0x%04x)",
+				  entry, le16_to_cpu(ES_FILE(es).checksum), chksum);
+			goto free_es;
+		}
 		for (i = 0; i * EXFAT_FILE_NAME_LEN < ES_STREAM(es).name_len; i++)
 			if (!exfat_get_validated_dentry(es, ES_INDEX_NAME + i, TYPE_NAME))
 				goto free_es;
-- 
2.25.1