linux-kernel - Re: [PATCH v2 2/2] fs: avoid fdput() after failed fdget() in kernel_read_file_from

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Message-ID: <20200513131335.GN11244@42.do-not-panic.com>
Date:   Wed, 13 May 2020 13:13:35 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>, keescook@...omium.org,
        Scott Branden <scott.branden@...adcom.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        linux-security-module@...r.kernel.org, jmorris@...ei.org,
        serge@...lyn.com, ast@...nel.org, daniel@...earbox.net,
        kafai@...com, songliubraving@...com, yhs@...com, andriin@...com,
        john.fastabend@...il.com, kpsingh@...omium.org
Cc:     Shuah Khan <skhan@...uxfoundation.org>, axboe@...nel.dk,
        zohar@...ux.vnet.ibm.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] fs: avoid fdput() after failed fdget() in
 kernel_read_file_from_fd()

On Wed, May 13, 2020 at 06:49:50AM +0100, Al Viro wrote:
> On Tue, May 12, 2020 at 01:43:05PM -0600, Shuah Khan wrote:
> > diff --git a/fs/exec.c b/fs/exec.c
> > index 06b4c550af5d..ea24bdce939d 100644
> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -1021,8 +1021,8 @@ int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
> >  		goto out;
> >  
> >  	ret = kernel_read_file(f.file, buf, size, max_size, id);
> > -out:
> >  	fdput(f);
> > +out:
> >  	return ret;
> 
> Incidentally, why is that thing exported?

Both kernel_read_file_from_fd() and kernel_read_file() are exported
because they have users, however kernel_read_file() only has security
stuff as a user. Do we want to get rid of the lsm hook for it?

I also have some non-posted patches which tucks away these kernel_read*()
exports under a symbol namespace, to avoid wide-spread use / abuse on
areas in the kernel, so I'd be happy to take this on if we want to
remove it export / lsm hook as part of my series. I did this as there
is another series of patches for a new driver which extend these family
of functions with a now pread() variant....

  Luis