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Subject[PATCH 3.16 090/178] ext4: lock the xattr block before checksuming it
3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@mit.edu>

commit dac7a4b4b1f664934e8b713f529b629f67db313c upstream.

We must lock the xattr block before calculating or verifying the
checksum in order to avoid spurious checksum failures.

https://bugzilla.kernel.org/show_bug.cgi?id=193661

Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/xattr.c | 65 +++++++++++++++++++++++++++------------------------------
1 file changed, 31 insertions(+), 34 deletions(-)

--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -139,31 +139,26 @@ static __le32 ext4_xattr_block_csum(stru
}

static int ext4_xattr_block_csum_verify(struct inode *inode,
- sector_t block_nr,
- struct ext4_xattr_header *hdr)
+ struct buffer_head *bh)
{
- if (ext4_has_metadata_csum(inode->i_sb) &&
- (hdr->h_checksum != ext4_xattr_block_csum(inode, block_nr, hdr)))
- return 0;
- return 1;
-}
-
-static void ext4_xattr_block_csum_set(struct inode *inode,
- sector_t block_nr,
- struct ext4_xattr_header *hdr)
-{
- if (!ext4_has_metadata_csum(inode->i_sb))
- return;
+ struct ext4_xattr_header *hdr = BHDR(bh);
+ int ret = 1;

- hdr->h_checksum = ext4_xattr_block_csum(inode, block_nr, hdr);
+ if (ext4_has_metadata_csum(inode->i_sb)) {
+ lock_buffer(bh);
+ ret = (hdr->h_checksum == ext4_xattr_block_csum(inode,
+ bh->b_blocknr, hdr));
+ unlock_buffer(bh);
+ }
+ return ret;
}

-static inline int ext4_handle_dirty_xattr_block(handle_t *handle,
- struct inode *inode,
- struct buffer_head *bh)
+static void ext4_xattr_block_csum_set(struct inode *inode,
+ struct buffer_head *bh)
{
- ext4_xattr_block_csum_set(inode, bh->b_blocknr, BHDR(bh));
- return ext4_handle_dirty_metadata(handle, inode, bh);
+ if (ext4_has_metadata_csum(inode->i_sb))
+ BHDR(bh)->h_checksum = ext4_xattr_block_csum(inode,
+ bh->b_blocknr, BHDR(bh));
}

static inline const struct xattr_handler *
@@ -224,7 +219,7 @@ ext4_xattr_check_block(struct inode *ino
if (BHDR(bh)->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC) ||
BHDR(bh)->h_blocks != cpu_to_le32(1))
return -EIO;
- if (!ext4_xattr_block_csum_verify(inode, bh->b_blocknr, BHDR(bh)))
+ if (!ext4_xattr_block_csum_verify(inode, bh))
return -EIO;
error = ext4_xattr_check_names(BFIRST(bh), bh->b_data + bh->b_size,
bh->b_data);
@@ -568,23 +563,22 @@ ext4_xattr_release_block(handle_t *handl
le32_add_cpu(&BHDR(bh)->h_refcount, -1);
if (ce)
mb_cache_entry_release(ce);
+ ext4_xattr_block_csum_set(inode, bh);
/*
* Beware of this ugliness: Releasing of xattr block references
* from different inodes can race and so we have to protect
* from a race where someone else frees the block (and releases
* its journal_head) before we are done dirtying the buffer. In
* nojournal mode this race is harmless and we actually cannot
- * call ext4_handle_dirty_xattr_block() with locked buffer as
+ * call ext4_handle_dirty_metadata() with locked buffer as
* that function can call sync_dirty_buffer() so for that case
* we handle the dirtying after unlocking the buffer.
*/
if (ext4_handle_valid(handle))
- error = ext4_handle_dirty_xattr_block(handle, inode,
- bh);
+ error = ext4_handle_dirty_metadata(handle, inode, bh);
unlock_buffer(bh);
if (!ext4_handle_valid(handle))
- error = ext4_handle_dirty_xattr_block(handle, inode,
- bh);
+ error = ext4_handle_dirty_metadata(handle, inode, bh);
if (IS_SYNC(inode))
ext4_handle_sync(handle);
dquot_free_block(inode, EXT4_C2B(EXT4_SB(inode->i_sb), 1));
@@ -812,13 +806,14 @@ ext4_xattr_block_set(handle_t *handle, s
ext4_xattr_cache_insert(ext4_mb_cache,
bs->bh);
}
+ ext4_xattr_block_csum_set(inode, bs->bh);
unlock_buffer(bs->bh);
if (error == -EIO)
goto bad_block;
if (!error)
- error = ext4_handle_dirty_xattr_block(handle,
- inode,
- bs->bh);
+ error = ext4_handle_dirty_metadata(handle,
+ inode,
+ bs->bh);
if (error)
goto cleanup;
goto inserted;
@@ -887,10 +882,11 @@ inserted:
le32_add_cpu(&BHDR(new_bh)->h_refcount, 1);
ea_bdebug(new_bh, "reusing; refcount now=%d",
le32_to_cpu(BHDR(new_bh)->h_refcount));
+ ext4_xattr_block_csum_set(inode, new_bh);
unlock_buffer(new_bh);
- error = ext4_handle_dirty_xattr_block(handle,
- inode,
- new_bh);
+ error = ext4_handle_dirty_metadata(handle,
+ inode,
+ new_bh);
if (error)
goto cleanup_dquot;
}
@@ -945,11 +941,12 @@ getblk_failed:
goto getblk_failed;
}
memcpy(new_bh->b_data, s->base, new_bh->b_size);
+ ext4_xattr_block_csum_set(inode, new_bh);
set_buffer_uptodate(new_bh);
unlock_buffer(new_bh);
ext4_xattr_cache_insert(ext4_mb_cache, new_bh);
- error = ext4_handle_dirty_xattr_block(handle,
- inode, new_bh);
+ error = ext4_handle_dirty_metadata(handle, inode,
+ new_bh);
if (error)
goto cleanup;
}
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