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mount-v2: workaround for multiple external bindmounts with no common root

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It's a problem when while restoring sharing group we need to copy
sharing between two mounts with non-intersecting roots, because kernel
does not allow it.

We have a case https://github.com/opencontainers/runc/pull/3442, where
runc adds different devtmpfs file-bindmounts to container and there is
no fsroot mount in container for this devtmpfs, thus mount-v2 faces the
above problem.

Luckily for the case of external mounts which are in one sharing group
and which have non-intersecting roots, these mounts likely only have
external master with no sharing, so we can just copy sharing from
external source and make it slave as a workaround.

https://github.com/checkpoint-restore/criu/issues/1886

Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
This commit is contained in:
Pavel Tikhomirov 2022-05-18 18:25:43 +03:00 • committed by Andrei Vagin
parent f8c9e07e4f
commit 229c5df5ce
1 changed files with 29 additions and 3 deletions
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32
criu/mount-v2.c
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@ -996,9 +996,35 @@ static int restore_one_sharing_group(struct sharing_group *sg)
if (other == first)
continue;
if (move_mount_set_group(first->mnt_fd_id, NULL, other->mnt_fd_id)) {
pr_err("Failed to copy sharing from %d to %d\n", first->mnt_id, other->mnt_id);
return -1;
if (is_sub_path(other->root, first->root)) {
if (move_mount_set_group(first->mnt_fd_id, NULL, other->mnt_fd_id)) {
pr_err("Failed to copy sharing from %d to %d\n", first->mnt_id, other->mnt_id);
return -1;
}
} else {
/*
* Case where mounts of this sharing group don't have common root.
* For instance we can create two sub-directories .a and .b in some
* shared mount, bindmount them separately somethere and umount the
* original mount. Now we have both bindmounts shared between each
* other. Kernel only allows to copy sharing between mounts when
* source root contains destination root, which is not true for
* these two, so we can't just copy from first to other.
*
* For external sharing (!sg->parent) with only master_id (shared_id
* == 0) we can workaround this by copying from their external source
* instead (same as we did for a first mount).
*
* This is a w/a runc usecase, see https://github.com/opencontainers/runc/pull/3442
*/
if (!sg->parent && !sg->shared_id) {
if (restore_one_sharing(sg, other))
return -1;
} else {
pr_err("Can't copy sharing from %d[%s] to %d[%s]\n", first->mnt_id, first->root,
other->mnt_id, other->root);
return -1;
}
}
}