linux-kernel - [PATCH] udf: Don't corrupt unalloc spacetable when writing it

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Message-Id: <1436292365-4395-1-git-send-email-steve@digidescorp.com>
Date:	Tue,  7 Jul 2015 13:06:05 -0500
From:	"Steven J. Magnani" <steve.magnani@...idescorp.com>
To:	jack@...e.cz
Cc:	linux-kernel@...r.kernel.org,
	"Steven J. Magnani" <steve@...idescorp.com>
Subject: [PATCH] udf: Don't corrupt unalloc spacetable when writing it

For a UDF filesystem configured with an Unallocated Space Table,
a filesystem operation that triggers an update to the table results
in on-disk corruption that prevents remounting:

  udf_read_tagged: tag version 0x0000 != 0x0002 || 0x0003, block 274

For example:
  1. Create a filesystem
      $ mkudffs --media-type=hd --blocksize=512 --lvid=BUGTEST \
              --vid=BUGTEST --fsid=BUGTEST --space=unalloctable \
              /dev/mmcblk0

  2. Mount it
      # mount /dev/mmcblk0 /mnt

  3. Create a file
      $ echo "No corruption, please" > /mnt/new.file

  4. Umount
      # umount /mnt

  5. Attempt remount
      # mount /dev/mmcblk0 /mnt

This appears to be a longstanding bug caused by zero-initialization of
the Unallocated Space Entry block buffer and only partial repopulation
of required fields before writing to disk. 

Commit 0adfb339fd64 ("udf: Fix unalloc space handling in udf_update_inode")
addressed one such field, but several others are required.

Signed-off-by: Steven J. Magnani <steve@...idescorp.com>
---
diff -uprN a/fs/udf/inode.c b/fs/udf/inode.c
--- a/fs/udf/inode.c	2015-07-06 13:42:08.861499890 -0500
+++ b/fs/udf/inode.c	2015-07-06 13:42:18.153499469 -0500
@@ -1652,17 +1652,9 @@ static int udf_update_inode(struct inode
 		       iinfo->i_ext.i_data, inode->i_sb->s_blocksize -
 					sizeof(struct unallocSpaceEntry));
 		use->descTag.tagIdent = cpu_to_le16(TAG_IDENT_USE);
-		use->descTag.tagLocation =
-				cpu_to_le32(iinfo->i_location.logicalBlockNum);
-		crclen = sizeof(struct unallocSpaceEntry) +
-				iinfo->i_lenAlloc - sizeof(struct tag);
-		use->descTag.descCRCLength = cpu_to_le16(crclen);
-		use->descTag.descCRC = cpu_to_le16(crc_itu_t(0, (char *)use +
-							   sizeof(struct tag),
-							   crclen));
-		use->descTag.tagChecksum = udf_tag_checksum(&use->descTag);
+		crclen = sizeof(struct unallocSpaceEntry);
 
-		goto out;
+		goto finish;
 	}
 
 	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_UID_FORGET))
@@ -1782,6 +1774,8 @@ static int udf_update_inode(struct inode
 		efe->descTag.tagIdent = cpu_to_le16(TAG_IDENT_EFE);
 		crclen = sizeof(struct extendedFileEntry);
 	}
+
+finish:
 	if (iinfo->i_strat4096) {
 		fe->icbTag.strategyType = cpu_to_le16(4096);
 		fe->icbTag.strategyParameter = cpu_to_le16(1);
@@ -1791,7 +1785,9 @@ static int udf_update_inode(struct inode
 		fe->icbTag.numEntries = cpu_to_le16(1);
 	}
 
-	if (S_ISDIR(inode->i_mode))
+	if (iinfo->i_use)
+		fe->icbTag.fileType = ICBTAG_FILE_TYPE_USE;
+	else if (S_ISDIR(inode->i_mode))
 		fe->icbTag.fileType = ICBTAG_FILE_TYPE_DIRECTORY;
 	else if (S_ISREG(inode->i_mode))
 		fe->icbTag.fileType = ICBTAG_FILE_TYPE_REGULAR;
@@ -1828,7 +1824,6 @@ static int udf_update_inode(struct inode
 						  crclen));
 	fe->descTag.tagChecksum = udf_tag_checksum(&fe->descTag);
 
-out:
 	set_buffer_uptodate(bh);
 	unlock_buffer(bh);
 
--
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