[Added Al Viro]
On Thu, Jan 4, 2018 at 6:20 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> Decoding an upper file handle is done by decoding the upper dentry from
> underlying upper fs, finding or allocating an overlay inode that is
> hashed by the real upper inode and instantiating an overlay dentry with
> that inode.
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/overlayfs/export.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++
> fs/overlayfs/namei.c | 4 +--
> fs/overlayfs/overlayfs.h | 2 ++
> 3 files changed, 95 insertions(+), 2 deletions(-)
>
> diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
> index 58c4f5e8a67e..5c72784a0b4d 100644
> --- a/fs/overlayfs/export.c
> +++ b/fs/overlayfs/export.c
> @@ -93,6 +93,97 @@ static int ovl_encode_inode_fh(struct inode *inode, u32 *fid, int *max_len,
> return type;
> }
>
> +/*
> + * Find or instantiate an overlay dentry from real dentries.
> + */
> +static struct dentry *ovl_obtain_alias(struct super_block *sb,
> + struct dentry *upper,
> + struct ovl_path *lowerpath)
> +{
> + struct inode *inode;
> + struct dentry *dentry;
> + struct ovl_entry *oe;
> +
> + /* TODO: obtain non pure-upper */
> + if (lowerpath)
> + return ERR_PTR(-EIO);
> +
> + inode = ovl_get_inode(sb, dget(upper), NULL, NULL, 0);
> + if (IS_ERR(inode)) {
> + dput(upper);
> + return ERR_CAST(inode);
> + }
> +
> + dentry = d_obtain_alias(inode);
> + if (IS_ERR(dentry) || dentry->d_fsdata)
Racing two instances of this code, each thinking it got a new alias
and trying to fill it, results in a memory leak.
Haven't checked in too much depth, but apparently other filesystems
are not affected, so we need something special here.
One solution: split d_instantiate_anon(dentry, inode) out of
__d_obtain_alias() and supply that with the already initialized
dentry.
Al?
Thanks,
Miklos
> + return dentry;
> +
> + oe = ovl_alloc_entry(0);
> + if (!oe) {
> + dput(dentry);
> + return ERR_PTR(-ENOMEM);
> + }
> +
> + dentry->d_fsdata = oe;
> + ovl_dentry_set_upper_alias(dentry);
> +
> + return dentry;
> +}
> +
> +static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
> + struct ovl_fh *fh)
> +{
> + struct ovl_fs *ofs = sb->s_fs_info;
> + struct dentry *dentry;
> + struct dentry *upper;
> +
> + if (!ofs->upper_mnt)
> + return ERR_PTR(-EACCES);
> +
> + upper = ovl_decode_fh(fh, ofs->upper_mnt);
> + if (IS_ERR_OR_NULL(upper))
> + return upper;
> +
> + dentry = ovl_obtain_alias(sb, upper, NULL);
> + dput(upper);
> +
> + return dentry;
> +}
> +
> +static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
> + int fh_len, int fh_type)
> +{
> + struct dentry *dentry = NULL;
> + struct ovl_fh *fh = (struct ovl_fh *) fid;
> + int len = fh_len << 2;
> + unsigned int flags = 0;
> + int err;
> +
> + err = -EINVAL;
> + if (fh_type != OVL_FILEID)
> + goto out_err;
> +
> + err = ovl_check_fh_len(fh, len);
> + if (err)
> + goto out_err;
> +
> + /* TODO: decode non-upper */
> + flags = fh->flags;
> + if (flags & OVL_FH_FLAG_PATH_UPPER)
> + dentry = ovl_upper_fh_to_d(sb, fh);
> + err = PTR_ERR(dentry);
> + if (IS_ERR(dentry) && err != -ESTALE)
> + goto out_err;
> +
> + return dentry;
> +
> +out_err:
> + pr_warn_ratelimited("overlayfs: failed to decode file handle (len=%d, type=%d, flags=%x, err=%i)\n",
> + len, fh_type, flags, err);
> + return ERR_PTR(err);
> +}
> +
> const struct export_operations ovl_export_operations = {
> .encode_fh = ovl_encode_inode_fh,
> + .fh_to_dentry = ovl_fh_to_dentry,
> };
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index a69cedf06000..87d39384dc55 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -107,7 +107,7 @@ static int ovl_acceptable(void *ctx, struct dentry *dentry)
> * Return -ENODATA for "origin unknown".
> * Return <0 for an invalid file handle.
> */
> -static int ovl_check_fh_len(struct ovl_fh *fh, int fh_len)
> +int ovl_check_fh_len(struct ovl_fh *fh, int fh_len)
> {
> if (fh_len < sizeof(struct ovl_fh) || fh_len < fh->len)
> return -EINVAL;
> @@ -171,7 +171,7 @@ static struct ovl_fh *ovl_get_origin_fh(struct dentry *dentry)
> goto out;
> }
>
> -static struct dentry *ovl_decode_fh(struct ovl_fh *fh, struct vfsmount *mnt)
> +struct dentry *ovl_decode_fh(struct ovl_fh *fh, struct vfsmount *mnt)
> {
> struct dentry *origin;
> int bytes;
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index f6fd999cb98e..c4f8e98e209e 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -258,6 +258,8 @@ static inline bool ovl_is_impuredir(struct dentry *dentry)
>
>
> /* namei.c */
> +int ovl_check_fh_len(struct ovl_fh *fh, int fh_len);
> +struct dentry *ovl_decode_fh(struct ovl_fh *fh, struct vfsmount *mnt);
> int ovl_verify_origin(struct dentry *dentry, struct dentry *origin,
> bool is_upper, bool set);
> int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index);
> --
> 2.7.4
>
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