From 229c5df5cefa4be44305ca08ae20befbb3d0f91d Mon Sep 17 00:00:00 2001 From: Pavel Tikhomirov Date: Wed, 18 May 2022 18:25:43 +0300 Subject: [PATCH] mount-v2: workaround for multiple external bindmounts with no common root 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 --- criu/mount-v2.c | 32 +++++++++++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-) diff --git a/criu/mount-v2.c b/criu/mount-v2.c index 1d188114f..5d53e9a22 100644 --- a/criu/mount-v2.c +++ b/criu/mount-v2.c @@ -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; + } } }