Demi Marie Obenour <demiobenour@gmail.com> writes:
On 11/2/25 07:43, Alyssa Ross wrote:
On Sun, Nov 02, 2025 at 01:18:02PM +0100, Alyssa Ross wrote:
Demi Marie Obenour <demiobenour@gmail.com> writes:
On 11/1/25 08:17, Alyssa Ross wrote:
Demi Marie Obenour <demiobenour@gmail.com> writes:
On 10/29/25 08:01, Alyssa Ross wrote: > Demi Marie Obenour <demiobenour@gmail.com> writes: > >> Spectrum OS's host has no network access. Updates must be downloaded by >> VMs. The downloads are placed into a bind-mounted directory. The VM >> can write whatever it wants into that directory. This includes symlinks >> that subsequent code might open, which would create a path traversal >> vulnerability. It also includes paths with names containing containing >> terminal escape sequences, newlines, or other nastiness. Furthermore, >> the directory should not have any subdirectories either. >> >> Add a simple C program that checks for such ugliness and indicates >> (via its exit code) if the VM misbehaved. It also ensures that both >> SHA256SUMS and SHA256SUMS.gpg are present. >> >> Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com> >> --- >> host/rootfs/Makefile | 6 +- >> lib/kcmdline-utils.mk | 6 ++ >> tools/default.nix | 1 + >> tools/meson.build | 1 + >> tools/updates-dir-check/meson.build | 4 ++ >> tools/updates-dir-check/updates-dir-check.c | 94 +++++++++++++++++++++++++++++ >> 6 files changed, 110 insertions(+), 2 deletions(-) > > I still don't really understand why this needs to be a C program instead > of find -H /path/to/dir -not -type f. None of the other checks seem > very necessary?
I trust this code more than I trust (especially) the Busybox implementation of find.
This doesn't really make sense to me. All of this is quite trivial find behaviour — not the sort of thing that's unlikely to have been widely tested. No objection to GNU find though if it helps.
I see: find with a -exec false to return an error if anything matching is found?
I'm way more familiar with C than with find, which is why I missed this.
Hmm, thinking about it some more I suppose there's a problem with find: there's no way to get it to exit as soon as it finds a matching file, with a failing error code, so it could end up running way too long.
So the C program is fine, I guess.
Actually, we can do it. We just need to make find not responsible for exiting.
foreground { pipeline { find -H /path/to/dir -mindepth 1 -not -type f -prune } grep -q . } importas -iu ? ? if { test $? -eq 1 } # We have only regular files.
When find prints a line, grep will exit, and find will receive SIGPIPE and exit.
This version also has a bug: if find exits with an error without printing anything, the exit status will be ignored. Something like this (not tested) might work:
pipeline { find -H /path/to/dir -mindepth 1 -not -type f -prune } importas -iu ! ! foreground { grep -q . } if { importas -iu ? ? test $? -eq 1 } wait $! importas -iu ? ? if { test $? -eq 0 }
However, it's all way way way way too subtle for me. It's short, but it's also extremely error-prone. The C program is longer, but it's also much easier to understand and modify.
Okay. :)