linux: open bind mount sources inside the rootfs at mount time - #2306
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A bind mount source inside the container rootfs refers to what is there at the time of the mount, including the mounts done before it. Yet such sources were opened beforehand, along with all the other bind mount sources (by the host with a user namespace, or before the first mount otherwise), so they referred to the rootfs as it was before any mounts. Do not open such sources beforehand. Instead, open them relative to the container rootfs when doing the mount. This does not work for idmapped mounts, which can only be created by the host. Add a test case. Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
kolyshkin
marked this pull request as ready for review
October 1, 2026 04:56
giuseppe
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Oct 1, 2026
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ah, I know about this difference with runc and hoped nobody noticed :-)
LGTM
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A bind mount source inside the container rootfs refers to what is there at the time of the mount, including the mounts done before it. Such sources were opened beforehand along with other bind mount sources (by the host with a user namespace, or before the first mount otherwise), so they referred to the rootfs as it was before any mounts.
Do not open such sources beforehand; open them relative to the container rootfs when doing the mount. This does not cover idmapped mounts, which can only be created by the host.
Adds a test case. The corresponding runc tests (
mounts.bats: runc run [mount order, container bind-mount source]with and without userns) can be enabled once opencontainers/runc#5503 is merged, as they currently use host rootfs paths as mount destinations.