linux-kernel - Re: [GIT PULL] overlayfs update for 5.15

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: <CAHk-=wiiYSSpmgLRaq+AXg5NjCh_02ShSXRxsa8CfoKa0OooEQ@mail.gmail.com>
Date:   Thu, 2 Sep 2021 09:35:24 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Miklos Szeredi <miklos@...redi.hu>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-unionfs@...r.kernel.org
Subject: Re: [GIT PULL] overlayfs update for 5.15

On Thu, Sep 2, 2021 at 6:51 AM Miklos Szeredi <miklos@...redi.hu> wrote:
>
> The reason this touches so many files is that the ->get_acl() method now
> gets a "bool rcu" argument.  The ->get_acl() API was updated based on
> comments from Al and Linus:
>
>   https://lore.kernel.org/linux-fsdevel/CAJfpeguQxpd6Wgc0Jd3ks77zcsAv_bn0q17L3VNnnmPKu11t8A@mail.gmail.com/

That link might have been good in the individual commit message too,
but I did it in the merge commit instead.

I did notice that we now have a stale comment about ->get_acl() in fs/namei.c:

                acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS);
                if (!acl)
                        return -EAGAIN;
                /* no ->get_acl() calls in RCU mode... */
                if (is_uncached_acl(acl))
                        return -ECHILD;

but we actually did the RCU-mode ->get_acl() call already in
get_cached_acl_rcu().

Of course, get_cached_acl_rcu() only does it for ACL_DONT_CACHE, not
for ACL_NOT_CACHED, so RCU mode is still a bit special.

At some point we probably should make get_cached_acl_rcu() do the
right thing for a successful lookup with ACL_NOT_CACHED set too, and
actually install the newly looked-up ACL. But I haven't thought much
about locking (but I think it would be ok, we use "cmpxchg" to update
the cached entry).

This is just a "maybe fixme for the future" note about that comment
and about get_cached_acl_rcu() behavior. I've pulled this, and I think
we're ok, it's just a small oddity.

                  Linus