NVIDIA / nvidia-container-toolkit / 34443089629

44%

main: 44%

Build Type

Pull #2059

github

Committed by klueska

Commit Message

update-ldcache hook: exec ldconfig from a sealed memfd

UpdateLDCache used to mount a fresh /proc inside the container root,
just so it could bind-mount the host ldconfig binary in through a
TOCTOU-safe /proc/self/fd/<n> target and then exec it by that same
path once pivoted.

This breaks under gVisor. Its createContainer hook doesn't have
permission to mount a new /proc inside the container, so mountProc
fails with EPERM. This constitutes a real regression, because this
hook worked fine before the changes described above were introduced.

To address this, UpdateLDCache now clones the host ldconfig binary
into a sealed, anonymous memfd (via libcontainer/exeseal.CloneBinary)
before touching any namespace or pivoting, then execs it by
descriptor with execveat(fd, "", ..., AT_EMPTY_PATH). A memfd has no
path and no mount-namespace membership, so it comes through
pivot_root untouched. We don't need to bind-mount anything into the
container, and we don't need to mount /proc anywhere.

This is also more isolated than before. Since ldconfig has no use
for /proc or /sys, prepareRoot now masks both with an empty tmpfs
before pivoting, if they're present in the container root, instead of
leaving a real working procfs mounted there and trusting ldconfig
never reads it.

We verified all of this against real GPU hardware through gVisor's
runsc runtime, as well as standard runc. `docker run --runtime=runsc
--device nvidia.com/gpu=0` against a non-Debian image resolves the
driver libraries and runs nvidia-smi correctly, confirming the hook
and the /proc/sys masking both work under gVisor's restricted-
namespace gofer process.

Signed-off-by: Kevin Klues <kklues@nvidia.com>

Pull Request Pull Request #2059: update-ldcache hook: exec ldconfig from a sealed memfd

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6 existing lines in 3 files now uncovered.

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