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SubjectRe: [PATCH 07/11] ovl: make ovl_create_real() cope with vfs_mkdir() safely
On Tue, May 29, 2018 at 5:41 PM, Miklos Szeredi <mszeredi@redhat.com> wrote:
> From: Amir Goldstein <amir73il@gmail.com>
>
> vfs_mkdir() may succeed and leave the dentry passed to it unhashed and
> negative. ovl_create_real() is the last caller breaking when that
> happens.
>
> [amir: split re-factoring of ovl_create_temp() to prep patch
> add comment about unhashed dir after mkdir
> add pr_warn() if mkdir succeeds and lookup fails]
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> ---
> fs/overlayfs/dir.c | 35 +++++++++++++++++++++++++++++++++--
> 1 file changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index 1b181292a624..b33d37d1a87c 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -114,6 +114,37 @@ int ovl_cleanup_and_whiteout(struct dentry *workdir, struct inode *dir,
> goto out;
> }
>
> +static struct dentry *ovl_mkdir_real(struct inode *dir, struct dentry *dentry,
> + umode_t mode)
> +{
> + int err;
> +
> + err = ovl_do_mkdir(dir, dentry, mode);
> + if (err) {
> + dput(dentry);
> + return ERR_PTR(err);
> + }
> +
> + /*
> + * vfs_mkdir() may succeed and leave the dentry passed
> + * to it unhashed and negative. If that happens, try to
> + * lookup a new hashed and positive dentry.
> + */
> + if (unlikely(d_unhashed(dentry))) {
> + struct dentry *d;
> +
> + d = lookup_one_len(dentry->d_name.name, dentry->d_parent,
> + dentry->d_name.len);
> + if (IS_ERR(d)) {
> + pr_warn("overlayfs: failed lookup after mkdir (%pd2, err=%i).\n",
> + dentry, err);
> + }
> + dput(dentry);
> + dentry = d;
> + }
> + return dentry;
> +}
> +
> struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
> struct ovl_cattr *attr)
> {
> @@ -135,8 +166,8 @@ struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
> break;
>
> case S_IFDIR:
> - err = ovl_do_mkdir(dir, newdentry, attr->mode);
> - break;
> + /* mkdir is special... */
> + return ovl_mkdir_real(dir, newdentry, attr->mode);
>

I like your version with the helper.
So do we not care about the WARN_ON below on non-instantiated dentry
for directories? or we don't need it at all?

Thanks,
Amir.

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