From: Eric Biggers <ebiggers@kernel.org>
To: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>, Chao Yu <chao@kernel.org>,
Theodore Ts'o <tytso@mit.edu>,
linux-f2fs-devel@lists.sourceforge.net,
linux-fsdevel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] f2fs: remove broken support for allocating DIO writes
Date: Tue, 17 Aug 2021 17:06:22 -0700 [thread overview]
Message-ID: <YRxO/tzo15OTfbaZ@gmail.com> (raw)
In-Reply-To: <YRwrDdcryfTH4Vwi@google.com>
On Tue, Aug 17, 2021 at 02:33:01PM -0700, Jaegeuk Kim wrote:
> On 08/17, Eric Biggers wrote:
> > On Tue, Aug 17, 2021 at 11:57:46AM -0700, Jaegeuk Kim wrote:
> > > On 08/17, Christoph Hellwig wrote:
> > > > On Mon, Aug 16, 2021 at 07:03:21PM -0700, Eric Biggers wrote:
> > > > > Freeing preallocated blocks on error would be better than nothing, although note
> > > > > that the preallocated blocks may have filled an arbitrary sequence of holes --
> > > > > so simply truncating past EOF would *not* be sufficient.
> > > > >
> > > > > But really filesystems need to be designed to never expose uninitialized data,
> > > > > even if I/O errors or a sudden power failure occurs. It is unfortunate that
> > > > > f2fs apparently wasn't designed with that goal in mind.
> > > > >
> > > > > In any case, I don't think we can proceed with any other f2fs direct I/O
> > > > > improvements until this data leakage bug can be solved one way or another. If
> > > > > my patch to remove support for allocating writes isn't acceptable and the
> > > > > desired solution is going to require some more invasive f2fs surgery, are you or
> > > > > Chao going to work on it? I'm not sure there's much I can do here.
> > > >
> > > > Btw, this is generally a problem for buffered I/O as well, although the
> > > > window for exposing uninitialized blocks on a crash tends to be smaller.
> > >
> > > How about adding a warning message when we meet an error with preallocated
> > > unwritten blocks? In the meantime, can we get the Eric's patches for iomap
> > > support? I feel that we only need to modify the preallocation and error
> > > handling parts?
> >
> > A warning message would do nothing to prevent uninitialized blocks from being
> > leaked to userspace.
>
> To give a signal that it's a known issue that we'll fix later.
>
This bug is concerning mainly because it's a security vulnerability: anyone with
read+write access to just one file on an f2fs filesystem can effectively read
all other files on that filesystem. A warning message wouldn't change that.
And even in the case of this bug breaking a non-malicious program, hardly anyone
reads kernel log messages anyway. If something is broken, having a log message
that says "yeah, this is broken, sorry" isn't going to accomplish much...
- Eric
WARNING: multiple messages have this Message-ID (diff)
From: Eric Biggers <ebiggers@kernel.org>
To: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Theodore Ts'o <tytso@mit.edu>,
stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net,
Christoph Hellwig <hch@infradead.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [f2fs-dev] [PATCH] f2fs: remove broken support for allocating DIO writes
Date: Tue, 17 Aug 2021 17:06:22 -0700 [thread overview]
Message-ID: <YRxO/tzo15OTfbaZ@gmail.com> (raw)
In-Reply-To: <YRwrDdcryfTH4Vwi@google.com>
On Tue, Aug 17, 2021 at 02:33:01PM -0700, Jaegeuk Kim wrote:
> On 08/17, Eric Biggers wrote:
> > On Tue, Aug 17, 2021 at 11:57:46AM -0700, Jaegeuk Kim wrote:
> > > On 08/17, Christoph Hellwig wrote:
> > > > On Mon, Aug 16, 2021 at 07:03:21PM -0700, Eric Biggers wrote:
> > > > > Freeing preallocated blocks on error would be better than nothing, although note
> > > > > that the preallocated blocks may have filled an arbitrary sequence of holes --
> > > > > so simply truncating past EOF would *not* be sufficient.
> > > > >
> > > > > But really filesystems need to be designed to never expose uninitialized data,
> > > > > even if I/O errors or a sudden power failure occurs. It is unfortunate that
> > > > > f2fs apparently wasn't designed with that goal in mind.
> > > > >
> > > > > In any case, I don't think we can proceed with any other f2fs direct I/O
> > > > > improvements until this data leakage bug can be solved one way or another. If
> > > > > my patch to remove support for allocating writes isn't acceptable and the
> > > > > desired solution is going to require some more invasive f2fs surgery, are you or
> > > > > Chao going to work on it? I'm not sure there's much I can do here.
> > > >
> > > > Btw, this is generally a problem for buffered I/O as well, although the
> > > > window for exposing uninitialized blocks on a crash tends to be smaller.
> > >
> > > How about adding a warning message when we meet an error with preallocated
> > > unwritten blocks? In the meantime, can we get the Eric's patches for iomap
> > > support? I feel that we only need to modify the preallocation and error
> > > handling parts?
> >
> > A warning message would do nothing to prevent uninitialized blocks from being
> > leaked to userspace.
>
> To give a signal that it's a known issue that we'll fix later.
>
This bug is concerning mainly because it's a security vulnerability: anyone with
read+write access to just one file on an f2fs filesystem can effectively read
all other files on that filesystem. A warning message wouldn't change that.
And even in the case of this bug breaking a non-malicious program, hardly anyone
reads kernel log messages anyway. If something is broken, having a log message
that says "yeah, this is broken, sorry" isn't going to accomplish much...
- Eric
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Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
next prev parent reply other threads:[~2021-08-18 0:06 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-28 1:51 [f2fs-dev] [PATCH] f2fs: remove broken support for allocating DIO writes Eric Biggers
2021-07-28 1:51 ` Eric Biggers
2021-07-30 19:17 ` [f2fs-dev] " Eric Biggers
2021-07-30 19:17 ` Eric Biggers
2021-07-30 22:12 ` [f2fs-dev] " Jaegeuk Kim
2021-07-30 22:12 ` Jaegeuk Kim
2021-07-30 22:19 ` Eric Biggers
2021-07-30 22:19 ` [f2fs-dev] " Eric Biggers
2021-07-31 1:05 ` Jaegeuk Kim
2021-07-31 1:05 ` [f2fs-dev] " Jaegeuk Kim
2021-07-31 1:18 ` Eric Biggers
2021-07-31 1:18 ` Eric Biggers
2021-07-31 2:46 ` Theodore Ts'o
2021-07-31 2:46 ` [f2fs-dev] " Theodore Ts'o
2021-08-02 4:39 ` Eric Biggers
2021-08-02 4:39 ` Eric Biggers
2021-08-02 9:00 ` Chao Yu
2021-08-02 9:00 ` [f2fs-dev] " Chao Yu
2021-08-02 18:23 ` Jaegeuk Kim
2021-08-02 18:23 ` Jaegeuk Kim
2021-08-03 1:19 ` [f2fs-dev] " Chao Yu
2021-08-03 1:19 ` Chao Yu
2021-08-03 1:34 ` [f2fs-dev] " Jaegeuk Kim
2021-08-03 1:34 ` Jaegeuk Kim
2021-08-17 2:03 ` [f2fs-dev] " Eric Biggers
2021-08-17 2:03 ` Eric Biggers
2021-08-17 5:42 ` [f2fs-dev] " Christoph Hellwig
2021-08-17 5:42 ` Christoph Hellwig
2021-08-17 18:57 ` Jaegeuk Kim
2021-08-17 18:57 ` [f2fs-dev] " Jaegeuk Kim
2021-08-17 20:27 ` Eric Biggers
2021-08-17 20:27 ` [f2fs-dev] " Eric Biggers
2021-08-17 21:33 ` Jaegeuk Kim
2021-08-17 21:33 ` Jaegeuk Kim
2021-08-18 0:06 ` Eric Biggers [this message]
2021-08-18 0:06 ` Eric Biggers
2021-08-20 9:35 ` Chao Yu
2021-08-20 9:35 ` [f2fs-dev] " Chao Yu
2021-08-20 18:11 ` Eric Biggers
2021-08-20 18:11 ` Eric Biggers
2021-08-20 22:01 ` [f2fs-dev] " Chao Yu
2021-08-20 22:01 ` Chao Yu
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