From 570487d3faf2a1d8a220e6ee10f472163123d7da Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Mon, 15 May 2017 14:42:07 -0500 Subject: [PATCH] mnt: In umount propagation reparent in a separate pass It was observed that in some pathlogical cases that the current code does not unmount everything it should. After investigation it was determined that the issue is that mnt_change_mntpoint can can change which mounts are available to be unmounted during mount propagation which is wrong. The trivial reproducer is: $ cat ./pathological.sh mount -t tmpfs test-base /mnt cd /mnt mkdir 1 2 1/1 mount --bind 1 1 mount --make-shared 1 mount --bind 1 2 mount --bind 1/1 1/1 mount --bind 1/1 1/1 echo grep test-base /proc/self/mountinfo umount 1/1 echo grep test-base /proc/self/mountinfo $ unshare -Urm ./pathological.sh The expected output looks like: 46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000 47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 49 54 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 50 53 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 51 49 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 54 47 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 53 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 52 50 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000 47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 The output without the fix looks like: 46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000 47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 49 54 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 50 53 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 51 49 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 54 47 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 53 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 52 50 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000 47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 52 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 That last mount in the output was in the propgation tree to be unmounted but was missed because the mnt_change_mountpoint changed it's parent before the walk through the mount propagation tree observed it. Cc: stable@vger.kernel.org Fixes: 1064f874abc0 ("mnt: Tuck mounts under others instead of creating shadow/side mounts.") Acked-by: Andrei Vagin Reviewed-by: Ram Pai Signed-off-by: "Eric W. Biederman" --- fs/mount.h | 1 + fs/namespace.c | 1 + fs/pnode.c | 35 ++++++++++++++++++++++++++++++----- 3 files changed, 32 insertions(+), 5 deletions(-) diff --git a/fs/mount.h b/fs/mount.h index bf1fda6eed8f..ede5a1d5cf99 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -58,6 +58,7 @@ struct mount { struct mnt_namespace *mnt_ns; /* containing namespace */ struct mountpoint *mnt_mp; /* where is it mounted */ struct hlist_node mnt_mp_list; /* list mounts with the same mountpoint */ + struct list_head mnt_reparent; /* reparent list entry */ #ifdef CONFIG_FSNOTIFY struct fsnotify_mark_connector __rcu *mnt_fsnotify_marks; __u32 mnt_fsnotify_mask; diff --git a/fs/namespace.c b/fs/namespace.c index 8bd3e4d448b9..51e49866e1fe 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -236,6 +236,7 @@ static struct mount *alloc_vfsmnt(const char *name) INIT_LIST_HEAD(&mnt->mnt_slave_list); INIT_LIST_HEAD(&mnt->mnt_slave); INIT_HLIST_NODE(&mnt->mnt_mp_list); + INIT_LIST_HEAD(&mnt->mnt_reparent); init_fs_pin(&mnt->mnt_umount, drop_mountpoint); } return mnt; diff --git a/fs/pnode.c b/fs/pnode.c index 5bc7896d122a..52aca0a118ff 100644 --- a/fs/pnode.c +++ b/fs/pnode.c @@ -439,7 +439,7 @@ static void mark_umount_candidates(struct mount *mnt) * NOTE: unmounting 'mnt' naturally propagates to all other mounts its * parent propagates to. */ -static void __propagate_umount(struct mount *mnt) +static void __propagate_umount(struct mount *mnt, struct list_head *to_reparent) { struct mount *parent = mnt->mnt_parent; struct mount *m; @@ -464,17 +464,38 @@ static void __propagate_umount(struct mount *mnt) */ topper = find_topper(child); if (topper) - mnt_change_mountpoint(child->mnt_parent, child->mnt_mp, - topper); + list_add_tail(&topper->mnt_reparent, to_reparent); - if (list_empty(&child->mnt_mounts)) { + if (topper || list_empty(&child->mnt_mounts)) { list_del_init(&child->mnt_child); + list_del_init(&child->mnt_reparent); child->mnt.mnt_flags |= MNT_UMOUNT; list_move_tail(&child->mnt_list, &mnt->mnt_list); } } } +static void reparent_mounts(struct list_head *to_reparent) +{ + while (!list_empty(to_reparent)) { + struct mount *mnt, *parent; + struct mountpoint *mp; + + mnt = list_first_entry(to_reparent, struct mount, mnt_reparent); + list_del_init(&mnt->mnt_reparent); + + /* Where should this mount be reparented to? */ + mp = mnt->mnt_mp; + parent = mnt->mnt_parent; + while (parent->mnt.mnt_flags & MNT_UMOUNT) { + mp = parent->mnt_mp; + parent = parent->mnt_parent; + } + + mnt_change_mountpoint(parent, mp, mnt); + } +} + /* * collect all mounts that receive propagation from the mount in @list, * and return these additional mounts in the same list. @@ -485,11 +506,15 @@ static void __propagate_umount(struct mount *mnt) int propagate_umount(struct list_head *list) { struct mount *mnt; + LIST_HEAD(to_reparent); list_for_each_entry_reverse(mnt, list, mnt_list) mark_umount_candidates(mnt); list_for_each_entry(mnt, list, mnt_list) - __propagate_umount(mnt); + __propagate_umount(mnt, &to_reparent); + + reparent_mounts(&to_reparent); + return 0; } -- 2.20.1