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Re: [netmod] Common etag, timestamp on all interfaces (draft-lindblad-netconf-transaction-id)

Kent Watsen <kent@watsen.net> Thu, 24 March 2022 23:24 UTC

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From: Kent Watsen <kent@watsen.net>
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Date: Thu, 24 Mar 2022 23:24:30 +0000
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Cc: Andy Bierman <andy@yumaworks.com>, =?utf-8?Q?Bal=C3=A1zs_Lengyel?= <balazs.lengyel=40ericsson.com@dmarc.ietf.org>, "netmod@ietf.org" <netmod@ietf.org>
To: Jan Lindblad <janl@tail-f.com>
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Subject: Re: [netmod] Common etag, timestamp on all interfaces (draft-lindblad-netconf-transaction-id)
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Hi Jan,

> On Mar 24, 2022, at 4:37 PM, Jan Lindblad <janl@tail-f.com> wrote:
> 
> f this isn't obvious, here's an example:
> 1. Client A sends an edit to the server If-Unmodified-Since t0. Successful. Receives a Last-Modified timestamp t1.
> 2. Client B sends a an edit to the server. Last-Modified timestamp on server is now t2.
> 3. Client A sends an edit to the server without If-Unmodified-Since. It just sets one tiny little leaf off in one corner. Successful. Received a Last-Modified timestamp t3.
> 4. Client A sends an edit to the server If-Unmodified-Since t3. Successful, but clobbers Client B's edit, leading to a misconfiguration, which opens a security hole.
> 
> This is because the If-Unmodified-Since uses less than or equal in its test. The ETag mechanism is not susceptible to this issue, as it uses an equality test.

I don't think this example is valid.   Skipping past the obvious programming error, the equivalency you're trying to make applies to Etags too.

1. Client A sends an edit to the server If-Match e0. Successful. Receives a ETag e1.
2. Client B sends a an edit to the server. ETag on server is now e2.
3. Client A sends an edit to the server without If-Match. It just sets one tiny little leaf off in one corner. Successful. Received a ETag e3.
4. Client A sends an edit to the server If-Match e3. Successful, but clobbers Client B's edit, leading to a misconfiguration, which opens a security hole.


Kent // contributor

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