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    SubjectRe: [f2fs-dev] [PATCH 2/6] f2fs: do not expose unwritten blocks to user by DIO
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    On 2021/11/17 5:45, Jaegeuk Kim wrote:
    > DIO preallocates physical blocks before writing data, but if an error occurrs
    > or power-cut happens, we can see block contents from the disk. This patch tries
    > to fix it by 1) turning to buffered writes for DIO into holes, 2) truncating
    > unwritten blocks from error or power-cut.
    >
    > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
    > ---
    > fs/f2fs/data.c | 5 ++++-
    > fs/f2fs/f2fs.h | 5 +++++
    > fs/f2fs/file.c | 24 +++++++++++++++++++++++-
    > 3 files changed, 32 insertions(+), 2 deletions(-)
    >
    > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
    > index 3b27fb7daa8b..7ac1a39fcad2 100644
    > --- a/fs/f2fs/data.c
    > +++ b/fs/f2fs/data.c
    > @@ -1543,8 +1543,11 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
    > flag != F2FS_GET_BLOCK_DIO);
    > err = __allocate_data_block(&dn,
    > map->m_seg_type);
    > - if (!err)
    > + if (!err) {
    > + if (flag == F2FS_GET_BLOCK_PRE_DIO)
    > + file_need_truncate(inode);
    > set_inode_flag(inode, FI_APPEND_WRITE);
    > + }
    > }
    > if (err)
    > goto sync_out;
    > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
    > index be871a79c634..14bea669f87e 100644
    > --- a/fs/f2fs/f2fs.h
    > +++ b/fs/f2fs/f2fs.h
    > @@ -654,6 +654,7 @@ enum {
    > #define FADVISE_KEEP_SIZE_BIT 0x10
    > #define FADVISE_HOT_BIT 0x20
    > #define FADVISE_VERITY_BIT 0x40
    > +#define FADVISE_TRUNC_BIT 0x80
    >
    > #define FADVISE_MODIFIABLE_BITS (FADVISE_COLD_BIT | FADVISE_HOT_BIT)
    >
    > @@ -681,6 +682,10 @@ enum {
    > #define file_is_verity(inode) is_file(inode, FADVISE_VERITY_BIT)
    > #define file_set_verity(inode) set_file(inode, FADVISE_VERITY_BIT)
    >
    > +#define file_should_truncate(inode) is_file(inode, FADVISE_TRUNC_BIT)
    > +#define file_need_truncate(inode) set_file(inode, FADVISE_TRUNC_BIT)
    > +#define file_dont_truncate(inode) clear_file(inode, FADVISE_TRUNC_BIT)
    > +
    > #define DEF_DIR_LEVEL 0
    >
    > enum {
    > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
    > index 4bf77a5bf998..ec8de0662437 100644
    > --- a/fs/f2fs/file.c
    > +++ b/fs/f2fs/file.c
    > @@ -960,10 +960,21 @@ int f2fs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
    > down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
    > filemap_invalidate_lock(inode->i_mapping);
    >
    > + /*
    > + * Truncate stale preallocated blocks used by the previous DIO.
    > + */
    > + if (file_should_truncate(inode)) {
    > + err = f2fs_truncate(inode);
    > + if (err)
    > + goto out_unlock;
    > + file_dont_truncate(inode);
    > + }
    > +
    > truncate_setsize(inode, attr->ia_size);
    >
    > if (attr->ia_size <= old_size)
    > err = f2fs_truncate(inode);
    > +out_unlock:
    > /*
    > * do not trim all blocks after i_size if target size is
    > * larger than i_size.
    > @@ -4257,6 +4268,13 @@ static int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *iter)
    > /* If it will be an out-of-place direct write, don't bother. */
    > if (dio && f2fs_lfs_mode(sbi))
    > return 0;
    > + /*
    > + * Don't preallocate holes aligned to DIO_SKIP_HOLES which turns into
    > + * buffered IO, if DIO meets any holes.
    > + */
    > + if (dio && i_size_read(inode) &&
    > + (F2FS_BYTES_TO_BLK(pos) < F2FS_BLK_ALIGN(i_size_read(inode))))
    > + return 0;
    >
    > /* No-wait I/O can't allocate blocks. */
    > if (iocb->ki_flags & IOCB_NOWAIT)
    > @@ -4366,10 +4384,14 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
    > if (preallocated > 0 && i_size_read(inode) < target_size) {
    > down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
    > filemap_invalidate_lock(inode->i_mapping);
    > - f2fs_truncate(inode);
    > + if (!f2fs_truncate(inode))
    > + file_dont_truncate(inode);
    > filemap_invalidate_unlock(inode->i_mapping);
    > up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
    > + } else {
    > + file_dont_truncate(inode);

    How about this case:

    - touch file
    - DIO write [0, 8kb] to file
    - preallocate 2 physical blocks
    - set FADVISE_TRUNC_BIT
    - SPO
    - BUFIO write [0, 4kb] to file
    - file_dont_truncate -- it leaks unwritten [4kb, 8kb] to user after
    truncating file to 8kb

    Thanks,

    > }
    > +
    > clear_inode_flag(inode, FI_PREALLOCATED_ALL);
    >
    > if (ret > 0)
    >

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