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SubjectRe: [PATCH] ext4: avoid exposure of stale data in ext4_punch_hole() -v2
On Fri 27-09-13 19:54:03, Maxim Patlasov wrote:
> While handling punch-hole fallocate, it's useless to truncate page cache
> before removing the range from extent tree (or block map in indirect case)
> because page cache can be re-populated (by read-ahead or read(2) or mmap-ed
> read) immediately after truncating page cache, but before updating extent
> tree (or block map). In that case the user will see stale data even after
> fallocate is completed.
>
> Changed in v2 (Thanks to Jan Kara):
> - Until the problem of data corruption resulting from pages backed by
> already freed blocks is fully resolved, the simple thing we can do now
> is to add another truncation of pagecache after punch hole is done.
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
> ---
> fs/ext4/inode.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0d424d7..2984ddf 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3621,6 +3621,12 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
> up_write(&EXT4_I(inode)->i_data_sem);
> if (IS_SYNC(inode))
> ext4_handle_sync(handle);
> +
> + /* Now release the pages again to reduce race window */
> + if (last_block_offset > first_block_offset)
> + truncate_pagecache_range(inode, first_block_offset,
> + last_block_offset);
> +
> inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
> ext4_mark_inode_dirty(handle, inode);
> out_stop:
>
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR


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