Re: Local information disclosure in apport and systemd-coredump

[Vegard Nossum <vegard.nossum () oracle com>]

On 03/06/2025 06:05, Solar Designer wrote:
> With the PID range reduced from the default of 4M down to 2K, PID reuse
> is quick even with simple fork().  I am getting frequent unix_chkpwd
> coredumps (without password hashes in them, which is as expected without
> inotify), but none of them are getting ACLs set for read by the user
> (unexpected - I thought I'd win this easier race once in a while), e.g.:

I admit I didn't look very closely at the specifics of this bug but
maybe you could use a setpid() technique like this one?

"""
newgrp: fix potential string injection

Since newgrp is setuid-root, any write() system calls it does in order
to print error messages will be done as the root user.

Unprivileged users can get newgrp to print essentially arbitrary strings
to any open file in this way by passing those strings as argv[0] when
calling execve(). For example:

    $ setpid() { (exec -a $1$'\n:' newgrp '' 
2>/proc/sys/kernel/ns_last_pid & wait) >/dev/null; }
    $ setpid 31000
    $ readlink /proc/self
    31001

This is not a vulnerability in newgrp; it is a bug in the Linux kernel.

However, this type of bug is not new [1] and it makes sense to try to
mitigate these types of bugs in userspace where possible.

[1]: https://lwn.net/Articles/476947/
"""

https://github.com/shadow-maint/shadow/commit/9df4801e0b65073cc8a9031b22a73532ef7fdc2c


Vegard