linux-kernel - Re: [PATCH] files: rcu free files

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20201209194938.GS7338@casper.infradead.org>
Date:   Wed, 9 Dec 2020 19:49:38 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jann@...jh.net>
Subject: Re: [PATCH] files: rcu free files_struct

On Wed, Dec 09, 2020 at 12:04:38PM -0600, Eric W. Biederman wrote:
> @@ -397,8 +397,9 @@ static struct fdtable *close_files(struct files_struct * files)
>  		set = fdt->open_fds[j++];
>  		while (set) {
>  			if (set & 1) {
> -				struct file * file = xchg(&fdt->fd[i], NULL);
> +				struct file * file = fdt->fd[i];
>  				if (file) {
> +					rcu_assign_pointer(fdt->fd[i], NULL);

Assuming this is safe, you can use RCU_INIT_POINTER() here because you're
storing NULL, so you don't need the wmb() before storing the pointer.