Messages in this thread | | | Date | Fri, 7 Jan 2022 19:35:56 -0800 | From | Jaegeuk Kim <> | Subject | Re: [PATCH 3/6] f2fs: do not expose unwritten blocks to user by DIO |
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On 01/07, Eric Biggers wrote: > On Fri, Jan 07, 2022 at 05:52:48PM -0800, Jaegeuk Kim wrote: > > On 01/07, Eric Biggers wrote: > > > Hi Jaegeuk, > > > > > > On Tue, Jan 04, 2022 at 01:24:16PM -0800, 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 | 27 ++++++++++++++++++--------- > > > > fs/f2fs/inode.c | 8 ++++++++ > > > > 4 files changed, 35 insertions(+), 10 deletions(-) > > > > > > Unfortunately, this patch doesn't completely fix the uninitialized data > > > exposure. The problem is that it only makes DIO writes fall back to buffered > > > writes for holes, and not for reserved blocks (NEW_ADDR). f2fs's reserved > > > blocks are *not* the same as the unwritten extents that other filesystems have; > > > f2fs's reserved blocks have to be turned into regular blocks before DIO can > > > write to them. That immediately exposes them to concurrent reads (at least > > > buffered reads, but I think DIO reads too). > > > > Isn't it resolved by i_size which gives the written blocks only? > > > > I'm not sure what you mean, but this is for non-extending writes, so i_size > isn't relevant.
Ah, do you mean the file has NEW_ADDR within i_size? If so, let me continue to investigate further based on the current -dev, as it's quite hard to remove the old commits.
> > - Eric
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