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SubjectRe: [PATCH 07/11] ovl: make ovl_create_real() cope with vfs_mkdir() safely
On Tue, May 29, 2018 at 5:29 PM, Amir Goldstein <amir73il@gmail.com> wrote:
> 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?

I think we do. Filesystems do all sorts of weird an unexpected
things. We should definitely not assume underlying filesystem
returns in any way sane result.

Fixed, thanks for spotting.

Miklos

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