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Subject[PATCH 5.0 035/238] fix cgroup_do_mount() handling of failure exits
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@zeniv.linux.org.uk>

commit 399504e21a10be16dd1408ba0147367d9d82a10c upstream.

same story as with last May fixes in sysfs (7b745a4e4051
"unfuck sysfs_mount()"); new_sb is left uninitialized
in case of early errors in kernfs_mount_ns() and papering
over it by treating any error from kernfs_mount_ns() as
equivalent to !new_ns ends up conflating the cases when
objects had never been transferred to a superblock with
ones when that has happened and resulting new superblock
had been dropped. Easily fixed (same way as in sysfs
case). Additionally, there's a superblock leak on
kernfs_node_dentry() failure *and* a dentry leak inside
kernfs_node_dentry() itself - the latter on probably
impossible errors, but the former not impossible to trigger
(as the matter of fact, injecting allocation failures
at that point *does* trigger it).

Cc: stable@kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/kernfs/mount.c | 8 ++++++--
kernel/cgroup/cgroup.c | 9 ++++++---
2 files changed, 12 insertions(+), 5 deletions(-)

--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -196,8 +196,10 @@ struct dentry *kernfs_node_dentry(struct
return dentry;

knparent = find_next_ancestor(kn, NULL);
- if (WARN_ON(!knparent))
+ if (WARN_ON(!knparent)) {
+ dput(dentry);
return ERR_PTR(-EINVAL);
+ }

do {
struct dentry *dtmp;
@@ -206,8 +208,10 @@ struct dentry *kernfs_node_dentry(struct
if (kn == knparent)
return dentry;
kntmp = find_next_ancestor(kn, knparent);
- if (WARN_ON(!kntmp))
+ if (WARN_ON(!kntmp)) {
+ dput(dentry);
return ERR_PTR(-EINVAL);
+ }
dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
strlen(kntmp->name));
dput(dentry);
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2033,7 +2033,7 @@ struct dentry *cgroup_do_mount(struct fi
struct cgroup_namespace *ns)
{
struct dentry *dentry;
- bool new_sb;
+ bool new_sb = false;

dentry = kernfs_mount(fs_type, flags, root->kf_root, magic, &new_sb);

@@ -2043,6 +2043,7 @@ struct dentry *cgroup_do_mount(struct fi
*/
if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
struct dentry *nsdentry;
+ struct super_block *sb = dentry->d_sb;
struct cgroup *cgrp;

mutex_lock(&cgroup_mutex);
@@ -2053,12 +2054,14 @@ struct dentry *cgroup_do_mount(struct fi
spin_unlock_irq(&css_set_lock);
mutex_unlock(&cgroup_mutex);

- nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
+ nsdentry = kernfs_node_dentry(cgrp->kn, sb);
dput(dentry);
+ if (IS_ERR(nsdentry))
+ deactivate_locked_super(sb);
dentry = nsdentry;
}

- if (IS_ERR(dentry) || !new_sb)
+ if (!new_sb)
cgroup_put(&root->cgrp);

return dentry;

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