linux-ext4 - Re: More ext4 acl/xattr corruption

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Date:	Thu, 14 May 2009 00:40:11 -0400
From:	Theodore Tso <tytso@....edu>
To:	Kevin Shanahan <kmshanah@...b.org.au>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: More ext4 acl/xattr corruption - 4th occurence now

On Wed, May 13, 2009 at 03:56:34PM +0930, Kevin Shanahan wrote:
> 
> Now, this is (possibly) interesting - that block contains a bunch of
> file data. Looks like a html email (I can tell it's email because of
> the FIXED_ prefix added to the tags by the mail sanitizer).

That is interesting.  Knowing that it is file data means we might be
able to track things down this way.

Are you able to apply the following patch to your kernel?  If so,
hopefully we'll be able to catch whatever is causing the problem in
the act.

						- Ted

commit 8ff799da106e9fc4da9b2a3753b5b86caab27f13
Author: Theodore Ts'o <tytso@....edu>
Date:   Thu May 14 00:39:48 2009 -0400

    ext4: Add a block validity check to ext4_get_blocks_wrap()
    
    A few users with very large disks have been reporting low block number
    filesystem corruptions, potentially zapping the block group
    descriptors or inodes in the first inode table block.  It's not clear
    what is causing this, but most recently, it appears that whatever is
    trashing the filesystem metadata appears to be file data.  So let's
    try to set a trap for the corruption in ext4_get_blocks_wrap(), which
    is where logical blocks in an inode are mapped to physical blocks.
    
    Signed-off-by: "Theodore Ts'o" <tytso@....edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4e7f363..4fad4fa 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1120,6 +1120,35 @@ static void ext4_da_update_reserve_space(struct inode *inode, int used)
 		ext4_discard_preallocations(inode);
 }
 
+static int check_block_validity(struct inode *inode, sector_t logical,
+				sector_t phys, int len)
+{
+	ext4_fsblk_t valid_block, itable_block;
+	struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
+	struct ext4_group_desc *gdp = ext4_get_group_desc(inode->i_sb, 0, 0);
+	unsigned int itable_len = EXT4_SB(inode->i_sb)->s_itb_per_group;
+
+	valid_block = le32_to_cpu(es->s_first_data_block) +
+		EXT4_SB(inode->i_sb)->s_gdb_count;
+	itable_block = ext4_inode_table(inode->i_sb, gdp);
+
+	if (unlikely((phys <= valid_block) ||
+		     ((phys + len - 1) > ext4_blocks_count(es)) ||
+		     ((phys >= itable_block) &&
+		      (phys <= itable_block + itable_len)) ||
+		     ((phys + len - 1 >= itable_block) &&
+		      (phys + len - 1 <= itable_block + itable_len)))) {
+		ext4_error(inode->i_sb, "check_block_validity",
+			   "inode #%lu logical block %llu mapped to %llu "
+			   "(size %d)", inode->i_ino,
+			   (unsigned long long) logical,
+			   (unsigned long long) phys, len);
+		WARN_ON(1);
+		return -EIO;
+	}
+	return 0;
+}
+
 /*
  * The ext4_get_blocks_wrap() function try to look up the requested blocks,
  * and returns if the blocks are already mapped.
@@ -1165,6 +1194,13 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
 	}
 	up_read((&EXT4_I(inode)->i_data_sem));
 
+	if (retval > 0 && buffer_mapped(bh)) {
+		int ret = check_block_validity(inode, block, 
+					       bh->b_blocknr, retval);
+		if (ret != 0)
+			return ret;
+	}
+
 	/* If it is only a block(s) look up */
 	if (!create)
 		return retval;
@@ -1241,6 +1277,12 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
 	}
 
 	up_write((&EXT4_I(inode)->i_data_sem));
+	if (retval > 0 && buffer_mapped(bh)) {
+		int ret = check_block_validity(inode, block, 
+					       bh->b_blocknr, retval);
+		if (ret != 0)
+			return ret;
+	}
 	return retval;
 }
 
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