From 813aae5bddcb2f8e34371cd5be44f8dcbfdf8a04 Mon Sep 17 00:00:00 2001 From: Tom Smeding Date: Thu, 8 Sep 2022 14:25:27 +0200 Subject: Add efault diagnosis, thanks int-e --- bugs/efault.html | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) (limited to 'bugs/efault.html') 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 @@

The impossible EFAULT

I have written a program; suppose it's called worker. -(While the program is written in Haskell, I don't think that's particularly relevant to this post.) -(EDIT: Reproducer can be found here.)

+(While the program is written in Haskell, I don't think that's particularly relevant to this post.)

+

(EDIT: Reproducer can be found here.)

+

(EDIT 2: Diagnosis by int-e on irc here.)

When run, worker 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 ./sleep.sh:

#!/bin/bash
@@ -41,5 +42,9 @@ Somehow, starting a script is different from starting a native process (and chan
 posix_spawnp shouldn't care what it is starting!
 That's the job of the loader, as far as I know.
 So what gives?

-
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.

+
The cause

+
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.

+
snap-server modifies the environment to set the locale, and setenv(3) is not atomic.
+In particular, it breaks execve(2) when they race, and this is what happens.
+All possible solutions to this problem are hacks.

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