From: Al Viro <viro@ZenIV.linux.org.uk>
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 0/9] overlay: fix inconsistency of ro file after copy-up
Date: Sun, 19 Feb 2017 09:14:41 +0000 [thread overview]
Message-ID: <20170219091430.GL29622@ZenIV.linux.org.uk> (raw)
In-Reply-To: <1487347778-18596-1-git-send-email-mszeredi@redhat.com>
On Fri, Feb 17, 2017 at 05:09:29PM +0100, Miklos Szeredi wrote:
> A file is opened for read-only, opened read-write (resulting in a copy up)
> and modified. The data read back from the the read-only fd will be stale
> in this case (the read-only file descriptor still refers to the lower,
> unmodified file).
>
> This patchset fixes issues related to this corner case. This is a
> requirement from various parties for accepting overlayfs as a "POSIX"
> filesystem.
>
> When an operation (read, mmap, fsync) is done on an overlay fd opened
> read-only that is referring to a lower file, check if it has been copied up
> in the mean time. If so, open the upper file and use that for the operation.
>
> To make the performance impact minimal for non-overlay case, use a flag in
> file->f_mode to indicate that this is an overlay file.
This is one hell of a DoS vector - it's really easy to eat tons of struct
file that way. Preparatory parts of that series make sense on their own,
but your "let's allocate a struct file, call ->open() and schedule that
struct file for closing upon the exit to userland on each kernel_read()"
is not.
next prev parent reply other threads:[~2017-02-19 9:15 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-17 16:09 [PATCH 0/9] overlay: fix inconsistency of ro file after copy-up Miklos Szeredi
2017-02-17 16:09 ` [PATCH 1/9] vfs: extract common parts of {compat_,}do_readv_writev() Miklos Szeredi
2017-02-17 16:09 ` [PATCH 2/9] vfs: pass type instead of fn to do_{loop,iter}_readv_writev() Miklos Szeredi
2017-02-17 16:09 ` [PATCH 3/9] vfs: use helpers for calling f_op->{read,write}_iter() Miklos Szeredi
2017-02-17 16:09 ` [PATCH 4/9] vfs: intercept reads to overlay files Miklos Szeredi
2017-02-19 9:05 ` Al Viro
2017-02-19 9:24 ` Miklos Szeredi
[not found] ` <D39694FF47DA2A43B120BF3DF6163E7A10CD2335@DGGEMA504-MBX.china.huawei.com>
2017-02-20 7:47 ` zhangyi (F)
2017-02-20 8:52 ` Miklos Szeredi
2017-02-17 16:09 ` [PATCH 5/9] mm: ovl: copy-up on MAP_SHARED Miklos Szeredi
2017-02-17 16:09 ` [PATCH 6/9] mm: use helper for calling f_op->mmap() Miklos Szeredi
2017-02-17 16:09 ` [PATCH 7/9] ovl: intercept mmap on overlay files Miklos Szeredi
2017-02-17 16:09 ` [PATCH 8/9] vfs: use helper for calling f_op->fsync() Miklos Szeredi
2017-02-17 16:09 ` [PATCH 9/9] vfs: intercept fsync on overlay files Miklos Szeredi
2017-02-19 9:14 ` Al Viro [this message]
2017-02-20 15:16 ` [PATCH 0/9] overlay: fix inconsistency of ro file after copy-up Miklos Szeredi
2017-03-07 16:26 ` Miklos Szeredi
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