From: David Miller <firstname.lastname@example.org>
Cc: email@example.com, firstname.lastname@example.org,
Subject: Re: [PATCH v2] ppp: remove the PPPIOCDETACH ioctl
Date: Thu, 24 May 2018 22:55:25 -0400 (EDT) [thread overview]
Message-ID: <email@example.com> (raw)
From: Eric Biggers <firstname.lastname@example.org>
Date: Wed, 23 May 2018 14:37:38 -0700
> From: Eric Biggers <email@example.com>
> The PPPIOCDETACH ioctl effectively tries to "close" the given ppp file
> before f_count has reached 0, which is fundamentally a bad idea. It
> does check 'f_count < 2', which excludes concurrent operations on the
> file since they would only be possible with a shared fd table, in which
> case each fdget() would take a file reference. However, it fails to
> account for the fact that even with 'f_count == 1' the file can still be
> linked into epoll instances. As reported by syzbot, this can trivially
> be used to cause a use-after-free.
> Yet, the only known user of PPPIOCDETACH is pppd versions older than
> ppp-2.4.2, which was released almost 15 years ago (November 2003).
> Also, PPPIOCDETACH apparently stopped working reliably at around the
> same time, when the f_count check was added to the kernel, e.g. see
> https://lkml.org/lkml/2002/12/31/83. Also, the current 'f_count < 2'
> check makes PPPIOCDETACH only work in single-threaded applications; it
> always fails if called from a multithreaded application.
> All pppd versions released in the last 15 years just close() the file
> descriptor instead.
> Therefore, instead of hacking around this bug by exporting epoll
> internals to modules, and probably missing other related bugs, just
> remove the PPPIOCDETACH ioctl and see if anyone actually notices. Leave
> a stub in place that prints a one-time warning and returns EINVAL.
> Reported-by: firstname.lastname@example.org
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Eric Biggers <email@example.com>
Applied and queued up for -stable.
next prev parent reply other threads:[~2018-05-25 2:55 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20180523032958.GE658@sol.localdomain>
2018-05-23 3:59 ` [PATCH] ppp: remove the PPPIOCDETACH ioctl Eric Biggers
2018-05-23 13:57 ` Guillaume Nault
2018-05-23 15:56 ` David Miller
2018-05-23 21:17 ` Eric Biggers
2018-05-23 21:37 ` [PATCH v2] " Eric Biggers
2018-05-23 23:04 ` Paul Mackerras
2018-05-24 14:04 ` Guillaume Nault
2018-05-25 2:55 ` David Miller [this message]
2018-06-06 9:01 ` Walter Harms
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