Date:	Mon, 28 Nov 2011 15:27:25 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Andreas Dilger <adilger.kernel@...ger.ca>,
	Theodore Tso <tytso@....edu>,
	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Sunil Mushran <sunil.mushran@...cle.com>,
	Martin K Petersen <martin.petersen@...cle.com>,
	Greg Freemyer <greg.freemyer@...il.com>,
	Amir Goldstein <amir73il@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Mingming Cao <cmm@...ibm.com>,
	Joel Becker <jlbec@...lplan.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, Coly Li <colyli@...il.com>
Subject: [PATCH 10/22] ext4: Verify and calculate checksums for extent tree
	blocks

Calculate and verify the checksum for each extent tree block.  The checksum is
located in the space immediately after the last possible ext4_extent in the
block.  The space is is typically the last 4-8 bytes in the block.

Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
---
 fs/ext4/ext4_extents.h |   25 +++++++++++++++++++++++-
 fs/ext4/extents.c      |   50 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+), 1 deletions(-)


diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
index a52db3a..56e891a 100644
--- a/fs/ext4/ext4_extents.h
+++ b/fs/ext4/ext4_extents.h
@@ -62,10 +62,22 @@
 /*
  * ext4_inode has i_block array (60 bytes total).
  * The first 12 bytes store ext4_extent_header;
- * the remainder stores an array of ext4_extent.
+ * the remainder stores an array of ext4_extent,
+ * followed by ext4_extent_tail.
  */
 
 /*
+ * This is the extent tail on-disk structure.
+ * All other extent structures are 12 bytes long.  It turns out that
+ * block_size % 12 >= 4 for all valid block sizes (1k, 2k, 4k).
+ * Therefore, this tail structure can be crammed into the end of the block
+ * without having to rebalance the tree.
+ */
+struct ext4_extent_tail {
+	__le32	et_checksum;	/* crc32c(uuid+inum+extent_block) */
+};
+
+/*
  * This is the extent on-disk structure.
  * It's used at the bottom of the tree.
  */
@@ -101,6 +113,17 @@ struct ext4_extent_header {
 
 #define EXT4_EXT_MAGIC		cpu_to_le16(0xf30a)
 
+#define EXT4_EXTENT_TAIL_OFFSET(hdr) \
+	(sizeof(struct ext4_extent_header) + \
+	 (sizeof(struct ext4_extent) * le16_to_cpu((hdr)->eh_max)))
+
+static inline struct ext4_extent_tail *
+find_ext4_extent_tail(struct ext4_extent_header *eh)
+{
+	return (struct ext4_extent_tail *)(((void *)eh) +
+					   EXT4_EXTENT_TAIL_OFFSET(eh));
+}
+
 /*
  * Array of ext4_ext_path contains path to some extent.
  * Creation/lookup routines use it for traversal/splitting/etc.
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 00f97f4..5db751e 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -45,6 +45,46 @@
 
 #include <trace/events/ext4.h>
 
+static __le32 ext4_extent_block_csum(struct inode *inode,
+				     struct ext4_extent_header *eh)
+{
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+	__u32 csum;
+
+	csum = ext4_chksum(sbi, ei->i_uuid_inum_csum, (__u8 *)eh,
+			   EXT4_EXTENT_TAIL_OFFSET(eh));
+	return cpu_to_le32(csum);
+}
+
+static int ext4_extent_block_csum_verify(struct inode *inode,
+					 struct ext4_extent_header *eh)
+{
+	struct ext4_extent_tail *et;
+
+	if (!EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
+		EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+		return 1;
+
+	et = find_ext4_extent_tail(eh);
+	if (et->et_checksum != ext4_extent_block_csum(inode, eh))
+		return 0;
+	return 1;
+}
+
+static void ext4_extent_block_csum_set(struct inode *inode,
+				       struct ext4_extent_header *eh)
+{
+	struct ext4_extent_tail *et;
+
+	if (!EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
+		EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+		return;
+
+	et = find_ext4_extent_tail(eh);
+	et->et_checksum = ext4_extent_block_csum(inode, eh);
+}
+
 static int ext4_split_extent(handle_t *handle,
 				struct inode *inode,
 				struct ext4_ext_path *path,
@@ -103,6 +143,7 @@ static int __ext4_ext_dirty(const char *where, unsigned int line,
 {
 	int err;
 	if (path->p_bh) {
+		ext4_extent_block_csum_set(inode, ext_block_hdr(path->p_bh));
 		/* path points to block */
 		err = __ext4_handle_dirty_metadata(where, line, handle,
 						   inode, path->p_bh);
@@ -375,6 +416,12 @@ static int __ext4_ext_check(const char *function, unsigned int line,
 		error_msg = "invalid extent entries";
 		goto corrupted;
 	}
+	/* Verify checksum on non-root extent tree nodes */
+	if (ext_depth(inode) != depth &&
+	    !ext4_extent_block_csum_verify(inode, eh)) {
+		error_msg = "extent tree corrupted";
+		goto corrupted;
+	}
 	return 0;
 
 corrupted:
@@ -914,6 +961,7 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
 		le16_add_cpu(&neh->eh_entries, m);
 	}
 
+	ext4_extent_block_csum_set(inode, neh);
 	set_buffer_uptodate(bh);
 	unlock_buffer(bh);
 
@@ -992,6 +1040,7 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
 				sizeof(struct ext4_extent_idx) * m);
 			le16_add_cpu(&neh->eh_entries, m);
 		}
+		ext4_extent_block_csum_set(inode, neh);
 		set_buffer_uptodate(bh);
 		unlock_buffer(bh);
 
@@ -1089,6 +1138,7 @@ static int ext4_ext_grow_indepth(handle_t *handle, struct inode *inode,
 	else
 		neh->eh_max = cpu_to_le16(ext4_ext_space_block(inode, 0));
 	neh->eh_magic = EXT4_EXT_MAGIC;
+	ext4_extent_block_csum_set(inode, neh);
 	set_buffer_uptodate(bh);
 	unlock_buffer(bh);
 

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