From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: Kernel crash in free_pipe_info()
Date: Tue, 31 Oct 2017 05:00:00 +0000 [thread overview]
Message-ID: <20171031050000.GK21978@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CA+55aFxwY6aLaKEifHwh6UZJ+6VR_XBA8B1w4SbnA+F8Cu2v6g@mail.gmail.com>
On Mon, Oct 30, 2017 at 08:06:23PM -0700, Linus Torvalds wrote:
> We do that "free_pipe_info(inode->i_pipe);", but we never actually
> clear inode->i_pipe, so now we have an inode that looks like a pipe
> inode, and has a stale pointer to a pipe_inode_info.
>
> It all looks technically correct. It's fine to use put_filp(), because
> the file pointer has never really been used. And the inode should
> never get re-used anyway without going through the whole reinit in
> inode_init_always().
>
> So I don't see anything *wrong*, but I see a lot that is just unusual,
FWIW, it's really brittle - consider
if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
i_readcount_inc(path->dentry->d_inode);
in alloc_file(). It's not the source of trouble in this case, but only
because it's the second call that gets FMODE_READ; reorder them in
create_pipe_files() and you've got a bug.
I considered using fput() there, but that would've required manually
decrementing pipe->files first, which made it rather unappealing...
I don't see anything relevant there, but that's not saying much - flu
and debugging do not mix well, and lack of sleep also doesn't help ;-/
next prev parent reply other threads:[~2017-10-31 5:00 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-30 20:58 Kernel crash in free_pipe_info() Cong Wang
2017-10-30 22:14 ` Linus Torvalds
2017-10-30 22:26 ` Linus Torvalds
2017-10-31 1:19 ` Cong Wang
2017-10-31 2:08 ` Linus Torvalds
2017-10-31 3:06 ` Linus Torvalds
2017-10-31 5:00 ` Al Viro [this message]
2017-10-31 4:44 ` Al Viro
2017-10-31 19:00 ` Linus Torvalds
2017-11-01 3:19 ` Cong Wang
2017-11-10 6:07 ` Simon Brewer
2017-11-10 19:16 ` Cong Wang
2017-11-10 19:47 ` Linus Torvalds
2017-10-31 1:28 ` Cong Wang
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