lkml.org 
[lkml]   [2017]   [Feb]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/9] overlay: fix inconsistency of ro file after copy-up
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.

\
 
 \ /
  Last update: 2017-02-19 10:15    [W:0.093 / U:0.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site