nspawn: actually mask certain files under /proc/#40833
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mrc0mmand wants to merge 1 commit intosystemd:mainfrom
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nspawn: actually mask certain files under /proc/#40833mrc0mmand wants to merge 1 commit intosystemd:mainfrom
mrc0mmand wants to merge 1 commit intosystemd:mainfrom
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/run/systemd/inaccessible/ exists only on host - in the container we have /run/host/inaccessible/, and since all the inaccessible mounts have MOUNT_IN_USERNS we need to use the latter one, otherwise the masking gets silently skipped: ~# SYSTEMD_LOG_LEVEL=debug systemd-nspawn -q --directory=foo ls -la /proc/kallsyms ... Bind-mounting /run/systemd/inaccessible/reg on /proc/kallsyms (MS_BIND "")... Failed to mount /run/systemd/inaccessible/reg (type n/a) on /proc/kallsyms (MS_BIND ""): No such file or directory Changing mount flags /proc/kallsyms (MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_REMOUNT|MS_BIND "")... Failed to mount n/a (type n/a) on /proc/kallsyms (MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_REMOUNT|MS_BIND ""): Invalid argument Bind-mounting /run/systemd/inaccessible/reg on /proc/kcore (MS_BIND "")... Failed to mount /run/systemd/inaccessible/reg (type n/a) on /proc/kcore (MS_BIND ""): No such file or directory Changing mount flags /proc/kcore (MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_REMOUNT|MS_BIND "")... Failed to mount n/a (type n/a) on /proc/kcore (MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_REMOUNT|MS_BIND ""): Invalid argument ... Inner child finished, invoking payload. -r--r--r--. 1 root root 0 Feb 25 13:19 /proc/kallsyms
yuwata
approved these changes
Mar 2, 2026
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Could you also add test case with |
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/run/systemd/inaccessible/ exists only on host - in the container we have
/run/host/inaccessible/, and since all the inaccessible mounts have
MOUNT_IN_USERNS we need to use the latter one, otherwise the masking
gets silently skipped:
Now, this has been broken for a long time (I guess since de40a30, /cc @poettering ). And due to this, some folks actually started relying on this behavior. I know this because I noticed this issue due to one such use case - recently we got an internal report that kernel folks can't build kernels in RHEL 8 mock environments when using the nspawn isolation, because
/proc/kallsymsis inaccessible there. That's before de40a30 and hence the masking works there as expected:But later RHEL/Fedora/systemd versions don't mask these files properly, so they're still readable, which won't be possible after fixing it. Unfortunately, I don't think there's currently a way how to "override" this masking to "unbreak" these use cases, as
--bind*=and friends won't work there (maybeSYSTEMD_NSPAWN_API_VFS_WRITABLE=yeswould work, but it's ugly and I'm not sure about all the implications). Not sure what to do in this case, but I suspect that this might affect Fedora kernel builds as well if fixed (/cc @keszybz).