From: Wolfgang Bumiller <w.bumiller@proxmox.com>
To: Gabriel Goller <g.goller@proxmox.com>
Cc: Proxmox Backup Server development discussion
<pbs-devel@lists.proxmox.com>
Subject: Re: [pbs-devel] [PATCH proxmox-backup] auth: add locking to `PbsAuthenticator` to avoid race conditions
Date: Mon, 3 Jun 2024 11:00:51 +0200 [thread overview]
Message-ID: <4jt24gf7mcf7mt4a6isoz3szpq5f3pqpflsj55ti2itprzwpyz@mie5xdspzcqb> (raw)
In-Reply-To: <20240523114647.g7tf64ins3hhh5e6@luna.proxmox.com>
On Thu, May 23, 2024 at 01:46:47PM GMT, Gabriel Goller wrote:
> On 23.05.2024 13:25, Shannon Sterz wrote:
> > currently we don't lock the shadow file when removing or storing a
> > password. by adding locking here we avoid a situation where storing
> > and/or removing a password concurrently could lead to a race
> > condition. in this scenario it is possible that a password isn't
> > persisted or a password isn't removed. we already do this for
> > the "token.shadow" file, so just use the same mechanism here.
> >
> > Signed-off-by: Shannon Sterz <s.sterz@proxmox.com>
>
> Is there any reason why the store_password function does not lock the
> shadow.json file?
I'm assuming you mean this as an alternative to having a separate file
for the locking. In this case the answer is yes: We use `repalce_file()`
to store the new version to make sure the update is atomic (and a
parallel `authenticat_user` does not read a *partial* file and fail).
When you hold a lock on a file and you *replace* it, the new file is a
separate thing with no lock on it. Old threads waiting for a lock on the
old file will continue when the lock is free, new threads waiting on the
lock on the new file will be able to acquire that simultaneously.
Iow.: you can't lock something you're *replacing*.
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next prev parent reply other threads:[~2024-06-03 9:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-23 11:25 Shannon Sterz
2024-05-23 11:46 ` Gabriel Goller
2024-05-23 12:06 ` Shannon Sterz
2024-06-03 9:00 ` Wolfgang Bumiller [this message]
2024-06-03 9:12 ` Gabriel Goller
2024-06-03 9:02 ` [pbs-devel] applied: " Wolfgang Bumiller
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