ext4: add missing validation of fast-commit record lengths

Validate the inode and filename lengths in fast-commit journal records
so that a malicious fast-commit journal cannot cause a crash by having
invalid values for these. Also validate EXT4_FC_TAG_DEL_RANGE.

Fixes: aa75f4d3daae ("ext4: main fast-commit commit path")
Cc: <[e-mail]> # v5.10+
Signed-off-by: Eric Biggers <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Theodore Ts'o <[e-mail]>

fs/ext4/fast_commit.c

···
 	kfree(sbi->s_fc_replay_state.fc_modified_inodes);
 }
 
-static inline bool ext4_fc_tag_len_isvalid(struct ext4_fc_tl *tl,
-					   u8 *val, u8 *end)
+static bool ext4_fc_value_len_isvalid(struct ext4_sb_info *sbi,
+				      int tag, int len)
 {
-	if (val + tl->fc_len > end)
-		return false;
-
-	/* Here only check ADD_RANGE/TAIL/HEAD which will read data when do
-	 * journal rescan before do CRC check. Other tags length check will
-	 * rely on CRC check.
-	 */
-	switch (tl->fc_tag) {
+	switch (tag) {
 	case EXT4_FC_TAG_ADD_RANGE:
-		return (sizeof(struct ext4_fc_add_range) == tl->fc_len);
-	case EXT4_FC_TAG_TAIL:
-		return (sizeof(struct ext4_fc_tail) <= tl->fc_len);
-	case EXT4_FC_TAG_HEAD:
-		return (sizeof(struct ext4_fc_head) == tl->fc_len);
+		return len == sizeof(struct ext4_fc_add_range);
 	case EXT4_FC_TAG_DEL_RANGE:
+		return len == sizeof(struct ext4_fc_del_range);
+	case EXT4_FC_TAG_CREAT:
 	case EXT4_FC_TAG_LINK:
 	case EXT4_FC_TAG_UNLINK:
-	case EXT4_FC_TAG_CREAT:
+		len -= sizeof(struct ext4_fc_dentry_info);
+		return len >= 1 && len <= EXT4_NAME_LEN;
 	case EXT4_FC_TAG_INODE:
+		len -= sizeof(struct ext4_fc_inode);
+		return len >= EXT4_GOOD_OLD_INODE_SIZE &&
+			len <= sbi->s_inode_size;
 	case EXT4_FC_TAG_PAD:
-	default:
-		return true;
+		return true; /* padding can have any length */
+	case EXT4_FC_TAG_TAIL:
+		return len >= sizeof(struct ext4_fc_tail);
+	case EXT4_FC_TAG_HEAD:
+		return len == sizeof(struct ext4_fc_head);
 	}
+	return false;
 }
 
 /*
···
 	     cur = cur + EXT4_FC_TAG_BASE_LEN + tl.fc_len) {
 		ext4_fc_get_tl(&tl, cur);
 		val = cur + EXT4_FC_TAG_BASE_LEN;
-		if (!ext4_fc_tag_len_isvalid(&tl, val, end)) {
+		if (tl.fc_len > end - val ||
+		    !ext4_fc_value_len_isvalid(sbi, tl.fc_tag, tl.fc_len)) {
 			ret = state->fc_replay_num_tags ?
 				JBD2_FC_REPLAY_STOP : -ECANCELED;
 			goto out_err;

fs/ext4/fast_commit.h

···
 	__u8 fc_dname[];
 };
 
-/* Value structure for EXT4_FC_TAG_INODE and EXT4_FC_TAG_INODE_PARTIAL. */
+/* Value structure for EXT4_FC_TAG_INODE. */
 struct ext4_fc_inode {
 	__le32 fc_ino;
 	__u8 fc_raw_inode[];