5.4-stable review patch. If anyone has any objections, please let me know.
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From: Pavel Tikhomirov ptikhomirov@virtuozzo.com
[ Upstream commit 9ffb14ef61bab83fa818736bf3e7e6b6e182e8e2 ]
Previously a sharing group (shared and master ids pair) can be only inherited when mount is created via bindmount. This patch adds an ability to add an existing private mount into an existing sharing group.
With this functionality one can first create the desired mount tree from only private mounts (without the need to care about undesired mount propagation or mount creation order implied by sharing group dependencies), and next then setup any desired mount sharing between those mounts in tree as needed.
This allows CRIU to restore any set of mount namespaces, mount trees and sharing group trees for a container.
We have many issues with restoring mounts in CRIU related to sharing groups and propagation: - reverse sharing groups vs mount tree order requires complex mounts reordering which mostly implies also using some temporary mounts (please see https://lkml.org/lkml/2021/3/23/569 for more info)
- mount() syscall creates tons of mounts due to propagation - mount re-parenting due to propagation - "Mount Trap" due to propagation - "Non Uniform" propagation, meaning that with different tricks with mount order and temporary children-"lock" mounts one can create mount trees which can't be restored without those tricks (see https://www.linuxplumbersconf.org/event/7/contributions/640/)
With this new functionality we can resolve all the problems with propagation at once.
Link: https://lore.kernel.org/r/20210715100714.120228-1-ptikhomirov@virtuozzo.com Cc: Eric W. Biederman ebiederm@xmission.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Christian Brauner christian.brauner@ubuntu.com Cc: Mattias Nissler mnissler@chromium.org Cc: Aleksa Sarai cyphar@cyphar.com Cc: Andrei Vagin avagin@gmail.com Cc: linux-fsdevel@vger.kernel.org Cc: linux-api@vger.kernel.org Cc: lkml linux-kernel@vger.kernel.org Co-developed-by: Andrei Vagin avagin@gmail.com Acked-by: Christian Brauner christian.brauner@ubuntu.com Signed-off-by: Pavel Tikhomirov ptikhomirov@virtuozzo.com Signed-off-by: Andrei Vagin avagin@gmail.com Signed-off-by: Christian Brauner christian.brauner@ubuntu.com Stable-dep-of: cffd0441872e ("use uniform permission checks for all mount propagation changes") Signed-off-by: Sasha Levin sashal@kernel.org --- fs/namespace.c | 77 +++++++++++++++++++++++++++++++++++++- include/uapi/linux/mount.h | 3 +- 2 files changed, 78 insertions(+), 2 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c index ee5a87061f20..3c1afe60d438 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2624,6 +2624,78 @@ static bool check_for_nsfs_mounts(struct mount *subtree) return ret; }
+static int do_set_group(struct path *from_path, struct path *to_path) +{ + struct mount *from, *to; + int err; + + from = real_mount(from_path->mnt); + to = real_mount(to_path->mnt); + + namespace_lock(); + + err = -EINVAL; + /* To and From must be mounted */ + if (!is_mounted(&from->mnt)) + goto out; + if (!is_mounted(&to->mnt)) + goto out; + + err = -EPERM; + /* We should be allowed to modify mount namespaces of both mounts */ + if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN)) + goto out; + if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN)) + goto out; + + err = -EINVAL; + /* To and From paths should be mount roots */ + if (from_path->dentry != from_path->mnt->mnt_root) + goto out; + if (to_path->dentry != to_path->mnt->mnt_root) + goto out; + + /* Setting sharing groups is only allowed across same superblock */ + if (from->mnt.mnt_sb != to->mnt.mnt_sb) + goto out; + + /* From mount root should be wider than To mount root */ + if (!is_subdir(to->mnt.mnt_root, from->mnt.mnt_root)) + goto out; + + /* From mount should not have locked children in place of To's root */ + if (has_locked_children(from, to->mnt.mnt_root)) + goto out; + + /* Setting sharing groups is only allowed on private mounts */ + if (IS_MNT_SHARED(to) || IS_MNT_SLAVE(to)) + goto out; + + /* From should not be private */ + if (!IS_MNT_SHARED(from) && !IS_MNT_SLAVE(from)) + goto out; + + if (IS_MNT_SLAVE(from)) { + struct mount *m = from->mnt_master; + + list_add(&to->mnt_slave, &m->mnt_slave_list); + to->mnt_master = m; + } + + if (IS_MNT_SHARED(from)) { + to->mnt_group_id = from->mnt_group_id; + list_add(&to->mnt_share, &from->mnt_share); + lock_mount_hash(); + set_mnt_shared(to); + unlock_mount_hash(); + } + + err = 0; +out: + namespace_unlock(); + return err; +} + static int do_move_mount(struct path *old_path, struct path *new_path) { struct mnt_namespace *ns; @@ -3583,7 +3655,10 @@ SYSCALL_DEFINE5(move_mount, if (ret < 0) goto out_to;
- ret = do_move_mount(&from_path, &to_path); + if (flags & MOVE_MOUNT_SET_GROUP) + ret = do_set_group(&from_path, &to_path); + else + ret = do_move_mount(&from_path, &to_path);
out_to: path_put(&to_path); diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h index 96a0240f23fe..535ca707dfd7 100644 --- a/include/uapi/linux/mount.h +++ b/include/uapi/linux/mount.h @@ -70,7 +70,8 @@ #define MOVE_MOUNT_T_SYMLINKS 0x00000010 /* Follow symlinks on to path */ #define MOVE_MOUNT_T_AUTOMOUNTS 0x00000020 /* Follow automounts on to path */ #define MOVE_MOUNT_T_EMPTY_PATH 0x00000040 /* Empty to path permitted */ -#define MOVE_MOUNT__MASK 0x00000077 +#define MOVE_MOUNT_SET_GROUP 0x00000100 /* Set sharing group instead */ +#define MOVE_MOUNT__MASK 0x00000177
/* * fsopen() flags.