linux-ext4 - [PATCH] libext2fs: correctly subtract xattr blocks on bigalloc filesystems

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Message-Id: <20170521062303.32296-1-ebiggers3@gmail.com>
Date:   Sat, 20 May 2017 23:23:03 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     linux-ext4@...r.kernel.org
Cc:     Theodore Ts'o <tytso@....edu>, Eric Biggers <ebiggers@...gle.com>
Subject: [PATCH] libext2fs: correctly subtract xattr blocks on bigalloc filesystems

From: Eric Biggers <ebiggers@...gle.com>

ext2fs_inode_data_blocks2() calculates an inode's data block count by
subtracting the external xattr block, if any, from the total blocks.
But on bigalloc filesystems, the xattr "block" is actually a whole
cluster, so ext2fs_inode_data_blocks2() would return a too-large value.

It seems this could have caused several different problems, but the one
I encountered was that xfstest generic/399 failed in the "bigalloc"
config because e2fsck incorrectly considered a symlink on the filesystem
to be corrupted at the end of the test.  This happened because e2fsck
incorrectly calculated a nonzero data block count for a "fast" symlink
with an external xattr block and therefore treated it as a "slow"
symlink, which failed validation.

Fix this by updating ext2fs_inode_data_blocks2() to subtract the cluster
size rather than the block size.

Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 lib/ext2fs/blknum.c                          |   2 +-
 tests/f_bigalloc_symlink_with_xattr/expect.1 |   7 +++++++
 tests/f_bigalloc_symlink_with_xattr/image.gz | Bin 0 -> 663 bytes
 tests/f_bigalloc_symlink_with_xattr/name     |   1 +
 tests/f_bigalloc_symlink_with_xattr/script   |   2 ++
 5 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 tests/f_bigalloc_symlink_with_xattr/expect.1
 create mode 100644 tests/f_bigalloc_symlink_with_xattr/image.gz
 create mode 100644 tests/f_bigalloc_symlink_with_xattr/name
 create mode 100644 tests/f_bigalloc_symlink_with_xattr/script

diff --git a/lib/ext2fs/blknum.c b/lib/ext2fs/blknum.c
index ac808490..aa0e9118 100644
--- a/lib/ext2fs/blknum.c
+++ b/lib/ext2fs/blknum.c
@@ -71,7 +71,7 @@ blk64_t ext2fs_inode_data_blocks2(ext2_filsys fs,
 	return (inode->i_blocks |
 		(ext2fs_has_feature_huge_file(fs->super) ?
 		 (__u64) inode->osd2.linux2.l_i_blocks_hi << 32 : 0)) -
-		(inode->i_file_acl ? fs->blocksize >> 9 : 0);
+		(inode->i_file_acl ? EXT2_CLUSTER_SIZE(fs->super) >> 9 : 0);
 }
 
 /*
diff --git a/tests/f_bigalloc_symlink_with_xattr/expect.1 b/tests/f_bigalloc_symlink_with_xattr/expect.1
new file mode 100644
index 00000000..0e6c199f
--- /dev/null
+++ b/tests/f_bigalloc_symlink_with_xattr/expect.1
@@ -0,0 +1,7 @@
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Pass 3: Checking directory connectivity
+Pass 4: Checking reference counts
+Pass 5: Checking group summary information
+test_filesys: 12/16 files (0.0% non-contiguous), 112/128 blocks
+Exit status is 0
diff --git a/tests/f_bigalloc_symlink_with_xattr/image.gz b/tests/f_bigalloc_symlink_with_xattr/image.gz
new file mode 100644
index 0000000000000000000000000000000000000000..cbd125dc25a59e6795363e4228c5c5a24e49eeb2
GIT binary patch
literal 663
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l$5;JWSR9`6W9skuRgoQNE`u2gr4w?!8Fp-~GX^F`1^_GgBJThI

literal 0
HcmV?d00001

diff --git a/tests/f_bigalloc_symlink_with_xattr/name b/tests/f_bigalloc_symlink_with_xattr/name
new file mode 100644
index 00000000..f612796f
--- /dev/null
+++ b/tests/f_bigalloc_symlink_with_xattr/name
@@ -0,0 +1 @@
+fast symlink with external xattr block on bigalloc filesystem
diff --git a/tests/f_bigalloc_symlink_with_xattr/script b/tests/f_bigalloc_symlink_with_xattr/script
new file mode 100644
index 00000000..8ab2b9c6
--- /dev/null
+++ b/tests/f_bigalloc_symlink_with_xattr/script
@@ -0,0 +1,2 @@
+ONE_PASS_ONLY="true"
+. $cmd_dir/run_e2fsck
-- 
2.13.0