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t=1629245184; bh=gZg1UtCJiztDrJ25z8aSbakGUsVL/7mPg4qd/KxqXkY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ogfKnf4KQ3JNLZVZESpD1EyBWo0GbhsrY8/MQkVTKYo65b3F8m5vrwe3YO2vZqcmx 0pF0O+4P6l8CBkfop9inJXEUQdeo0CEF7Ihm5vM4mwCEftxm8+QKhyRg26aZg71wUX 4wzrbNErM3S77UkY+9TMfeHmAVZ4G5GmmDfobGhIvFZLL83FZwO6bJK/4KZl2lDp1c /WNZJL8Gp4TMrWZKGZVCKFAehpnqH5UwAmC3TGl3EqYxyL1zzNC+GlB3Q1OSjmRrw/ 34ULnyfNmuEtNITqAVkAHD8oZVCyHVEMbqPYHBKOxy8TsGNm1ePd2H2pL9L4mZ2eHv O4N+2F2y5RFVA== Date: Tue, 17 Aug 2021 17:06:22 -0700 From: Eric Biggers To: Jaegeuk Kim Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Headers-End: 1mG96D-009qlr-GC Subject: Re: [f2fs-dev] [PATCH] f2fs: remove broken support for allocating DIO writes X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Theodore Ts'o , stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Christoph Hellwig , linux-fsdevel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net 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 _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel