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Subject[26/34] ext4: Avoid data / filesystem corruption when write fails to copy data
2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------
(cherry picked from commit b9a4207d5e911b938f73079a83cc2ae10524ec7f)

When ext4_write_begin fails after allocating some blocks or
generic_perform_write fails to copy data to write, we truncate blocks
already instantiated beyond i_size. Although these blocks were never
inside i_size, we have to truncate the pagecache of these blocks so
that corresponding buffers get unmapped. Otherwise subsequent
__block_prepare_write (called because we are retrying the write) will
find the buffers mapped, not call ->get_block, and thus the page will
be backed by already freed blocks leading to filesystem and data
corruption.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/ext4/inode.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1534,6 +1534,16 @@ static int do_journal_get_write_access(h
return ext4_journal_get_write_access(handle, bh);
}

+/*
+ * Truncate blocks that were not used by write. We have to truncate the
+ * pagecache as well so that corresponding buffers get properly unmapped.
+ */
+static void ext4_truncate_failed_write(struct inode *inode)
+{
+ truncate_inode_pages(inode->i_mapping, inode->i_size);
+ ext4_truncate(inode);
+}
+
static int ext4_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata)
@@ -1599,7 +1609,7 @@ retry:

ext4_journal_stop(handle);
if (pos + len > inode->i_size) {
- ext4_truncate(inode);
+ ext4_truncate_failed_write(inode);
/*
* If truncate failed early the inode might
* still be on the orphan list; we need to
@@ -1709,7 +1719,7 @@ static int ext4_ordered_write_end(struct
ret = ret2;

if (pos + len > inode->i_size) {
- ext4_truncate(inode);
+ ext4_truncate_failed_write(inode);
/*
* If truncate failed early the inode might still be
* on the orphan list; we need to make sure the inode
@@ -1751,7 +1761,7 @@ static int ext4_writeback_write_end(stru
ret = ret2;

if (pos + len > inode->i_size) {
- ext4_truncate(inode);
+ ext4_truncate_failed_write(inode);
/*
* If truncate failed early the inode might still be
* on the orphan list; we need to make sure the inode
@@ -1814,7 +1824,7 @@ static int ext4_journalled_write_end(str
if (!ret)
ret = ret2;
if (pos + len > inode->i_size) {
- ext4_truncate(inode);
+ ext4_truncate_failed_write(inode);
/*
* If truncate failed early the inode might still be
* on the orphan list; we need to make sure the inode
@@ -3091,7 +3101,7 @@ retry:
* i_size_read because we hold i_mutex.
*/
if (pos + len > inode->i_size)
- ext4_truncate(inode);
+ ext4_truncate_failed_write(inode);
}

if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))



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