diff options
| author | Tom Smeding <tom@tomsmeding.com> | 2022-09-08 14:25:27 +0200 |
|---|---|---|
| committer | Tom Smeding <tom@tomsmeding.com> | 2022-09-08 14:25:27 +0200 |
| commit | 813aae5bddcb2f8e34371cd5be44f8dcbfdf8a04 (patch) | |
| tree | 2bd99d6dd9671b5628f2da729252f968c8629030 /bugs/efault.html | |
| parent | f4288dd09a9be0dad2cf955695d66d1b37c107d2 (diff) | |
Add efault diagnosis, thanks int-e
Diffstat (limited to 'bugs/efault.html')
| -rw-r--r-- | bugs/efault.html | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/bugs/efault.html b/bugs/efault.html index d00a51c..6aceda4 100644 --- a/bugs/efault.html +++ b/bugs/efault.html @@ -1,7 +1,8 @@ <h2>The impossible EFAULT</h2> <p>I have written a program; suppose it's called <code>worker</code>. -(While the program is written in Haskell, I don't think that's particularly relevant to this post.) -(EDIT: Reproducer can be found <a href="https://git.tomsmeding.com/snap-efault/tree/">here</a>.)</p> +(While the program is written in Haskell, I don't think that's particularly relevant to this post.)</p> +<p>(EDIT: Reproducer can be found <a href="https://git.tomsmeding.com/snap-efault/tree/">here</a>.)</p> +<p>(EDIT 2: Diagnosis by <code>int-e</code> on irc <a href="https://paste.tomsmeding.com/D22SvR2T">here</a>.)</p> <p>When run, <code>worker</code> starts a bunch of copies of a script. Under normal circumstances this script sets up a container using Linux cgroups and Linux user namespaces, but none of that is relevant because the strange behaviour in question occurs just fine without all of that -- in fact, we'll let it start the following script, say <code>./sleep.sh</code>:</p> <pre><code class="language-bash">#!/bin/bash @@ -41,5 +42,9 @@ Somehow, starting a script is different from starting a native process (and chan <code>posix_spawnp</code> shouldn't care what it is starting! That's the job of the loader, as far as I know. So what gives?</p> -<p>I'll try to reduce my own program to a minimal reproducer, and if I find anything I'll post an update to this post. -In the meantime, spookiness.</p> +<h3>The cause</h3> +<p><s>I'll try to reduce my own program to a minimal reproducer, and if I find anything I'll post an update to this post. +In the meantime, spookiness.</s></p> +<p><code>snap-server</code> <a href="https://github.com/snapframework/snap-server/blob/8d89c10014d8d295bfbf5419bbb8551de32d7f85/src/Snap/Http/Server.hs#L161">modifies the environment</a> to set the locale, and <code>setenv(3)</code> is not atomic. +In particular, it breaks <code>execve(2)</code> when they race, and this is what happens. +All possible solutions to this problem are hacks.</p> |