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authorEric W. Biederman <ebiederm@xmission.com>2017-05-15 14:42:07 -0500
committerEric W. Biederman <ebiederm@xmission.com>2017-05-23 08:40:32 -0500
commit570487d3faf2a1d8a220e6ee10f472163123d7da (patch)
tree185995239e9eddcc5c0a3e1e2d88aede25455c0b /fs/pnode.c
parentc70d9d809fdeecedb96972457ee45c49a232d97f (diff)
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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 <avagin@virtuozzo.com> Reviewed-by: Ram Pai <linuxram@us.ibm.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'fs/pnode.c')
-rw-r--r--fs/pnode.c35
1 files changed, 30 insertions, 5 deletions
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;
}