This is needed to properly stack overlay filesystems, I.E, being able
to create a whiteout file on an overlay mount and then use that as
part of the lowerdir in another overlay mount.
The way this works is that we create a regular whiteout, but set the
`overlay.nowhiteout` xattr on it. Whenever we check if a file is a
whiteout we check this xattr and don't treat it as a whiteout if it is
set. The xattr itself is then stripped and when viewed as part of the
overlayfs mount it looks like a regular whiteout.
In order to make the creation of the whiteout file with xattr atomic
we always take ovl_create_over_whiteout() codepath when creating
whiteouts.
Signed-off-by: Alexander Larsson <alexl@xxxxxxxxxx>
---
fs/overlayfs/dir.c | 24 +++++++++++++++++-------
fs/overlayfs/namei.c | 14 +++++++++-----
fs/overlayfs/overlayfs.h | 13 +++++++++++++
fs/overlayfs/readdir.c | 7 ++++++-
fs/overlayfs/super.c | 2 +-
fs/overlayfs/util.c | 20 ++++++++++++++++++++
6 files changed, 66 insertions(+), 14 deletions(-)
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 033fc0458a3d..2f3442f5430d 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -442,6 +442,11 @@ static int ovl_set_upper_acl(struct ovl_fs *ofs, struct dentry *upperdentry,
return ovl_do_set_acl(ofs, upperdentry, acl_name, acl);
}
+static bool ovl_cattr_is_whiteout(struct ovl_cattr *attr)
+{
+ return S_ISCHR(attr->mode) && attr->rdev == WHITEOUT_DEV;
+}
+
static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
struct ovl_cattr *cattr)
{
@@ -477,7 +482,8 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
goto out_unlock;
err = -ESTALE;
- if (d_is_negative(upper) || !IS_WHITEOUT(d_inode(upper)))
+ if (!ovl_cattr_is_whiteout(cattr) &&
+ (d_is_negative(upper) || !ovl_upper_is_whiteout(ofs, upper)))
goto out_dput;
newdentry = ovl_create_temp(ofs, workdir, cattr);
@@ -485,6 +491,13 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
if (IS_ERR(newdentry))
goto out_dput;
+ if (ovl_cattr_is_whiteout(cattr)) {
+ err = ovl_setxattr(ofs, newdentry, OVL_XATTR_NOWHITEOUT,
+ NULL, 0);
+ if (err < 0)
+ goto out_cleanup;
+ }
+
/*
* mode could have been mutilated due to umask (e.g. sgid directory)
*/
@@ -606,7 +619,8 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
put_cred(override_cred);
}
- if (!ovl_dentry_is_whiteout(dentry))
+ /* Create whiteouts in workdir so we can atomically set nowiteout xattr */
+ if (!ovl_dentry_is_whiteout(dentry) && !ovl_cattr_is_whiteout(attr))
err = ovl_create_upper(dentry, inode, attr);
else
err = ovl_create_over_whiteout(dentry, inode, attr);
@@ -669,10 +683,6 @@ static int ovl_mkdir(struct mnt_idmap *idmap, struct inode *dir,
static int ovl_mknod(struct mnt_idmap *idmap, struct inode *dir,
struct dentry *dentry, umode_t mode, dev_t rdev)
{
- /* Don't allow creation of "whiteout" on overlay */
- if (S_ISCHR(mode) && rdev == WHITEOUT_DEV)
- return -EPERM;
-
return ovl_create_object(dentry, mode, rdev, NULL);
}
@@ -1219,7 +1229,7 @@ static int ovl_rename(struct mnt_idmap *idmap, struct inode *olddir,
}
} else {
if (!d_is_negative(newdentry)) {
- if (!new_opaque || !ovl_is_whiteout(newdentry))
+ if (!new_opaque || !ovl_upper_is_whiteout(ofs, newdentry))
goto out_dput;
} else {
if (flags & RENAME_EXCHANGE)
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 80391c687c2a..e90167789a13 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -251,7 +251,9 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
err = -EREMOTE;
goto out_err;
}
- if (ovl_is_whiteout(this)) {
+ path.dentry = this;
+ path.mnt = d->mnt;
+ if (ovl_path_is_whiteout(OVL_FS(d->sb), &path)) {
d->stop = d->opaque = true;
goto put_and_out;
}
@@ -264,8 +266,6 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
goto put_and_out;
}
- path.dentry = this;
- path.mnt = d->mnt;
if (!d_can_lookup(this)) {
if (d->is_dir || !last_element) {
d->stop = true;
@@ -438,7 +438,7 @@ int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
else if (IS_ERR(origin))
return PTR_ERR(origin);
- if (upperdentry && !ovl_is_whiteout(upperdentry) &&
+ if (upperdentry && !ovl_upper_is_whiteout(ofs, upperdentry) &&
inode_wrong_type(d_inode(upperdentry), d_inode(origin)->i_mode))
goto invalid;
@@ -1383,7 +1383,11 @@ bool ovl_lower_positive(struct dentry *dentry)
break;
}
} else {
- positive = !ovl_is_whiteout(this);
+ struct path path = {
+ .dentry = this,
+ .mnt = parentpath->layer->mnt,
+ };
+ positive = !ovl_path_is_whiteout(OVL_FS(dentry->d_sb), &path);
done = true;
dput(this);
}
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 311e1f37ce84..33d4c0011bb9 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -49,6 +49,7 @@ enum ovl_xattr {
OVL_XATTR_UUID,
OVL_XATTR_METACOPY,
OVL_XATTR_PROTATTR,
+ OVL_XATTR_NOWHITEOUT,
};
enum ovl_inode_flag {
@@ -469,16 +470,28 @@ void ovl_inode_update(struct inode *inode, struct dentry *upperdentry);
void ovl_dir_modified(struct dentry *dentry, bool impurity);
u64 ovl_inode_version_get(struct inode *inode);
bool ovl_is_whiteout(struct dentry *dentry);
+bool ovl_path_is_whiteout(struct ovl_fs *ofs, const struct path *path);
struct file *ovl_path_open(const struct path *path, int flags);
int ovl_copy_up_start(struct dentry *dentry, int flags);
void ovl_copy_up_end(struct dentry *dentry);
bool ovl_already_copied_up(struct dentry *dentry, int flags);
bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
enum ovl_xattr ox);
+bool ovl_path_check_nowhiteout_xattr(struct ovl_fs *ofs, const struct path *path);
bool ovl_path_check_origin_xattr(struct ovl_fs *ofs, const struct path *path);
bool ovl_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
const struct path *upperpath);
+static inline bool ovl_upper_is_whiteout(struct ovl_fs *ofs,
+ struct dentry *upperdentry)
+{
+ struct path upperpath = {
+ .dentry = upperdentry,
+ .mnt = ovl_upper_mnt(ofs),
+ };
+ return ovl_path_is_whiteout(ofs, &upperpath);
+}
+
static inline bool ovl_check_origin_xattr(struct ovl_fs *ofs,
struct dentry *upperdentry)
{
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index de39e067ae65..9cf8e7e2961c 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -280,7 +280,12 @@ static int ovl_check_whiteouts(const struct path *path, struct ovl_readdir_data
rdd->first_maybe_whiteout = p->next_maybe_whiteout;
dentry = lookup_one(mnt_idmap(path->mnt), p->name, dir, p->len);
if (!IS_ERR(dentry)) {
- p->is_whiteout = ovl_is_whiteout(dentry);
+ struct path childpath = {
+ .dentry = dentry,
+ .mnt = path->mnt,
+ };
+ p->is_whiteout = ovl_path_is_whiteout(OVL_FS(rdd->dentry->d_sb),
+ &childpath);
dput(dentry);
}
}
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index a3be13306c73..995c21349bb9 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -579,7 +579,7 @@ static int ovl_check_rename_whiteout(struct ovl_fs *ofs)
if (IS_ERR(whiteout))
goto cleanup_temp;
- err = ovl_is_whiteout(whiteout);
+ err = ovl_upper_is_whiteout(ofs, whiteout);
/* Best effort cleanup of whiteout and temp file */
if (err)
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 0f387092450e..da6d2abf64dd 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -575,6 +575,16 @@ bool ovl_is_whiteout(struct dentry *dentry)
return inode && IS_WHITEOUT(inode);
}
+/*
+ * Use this over ovl_is_whiteout for upper and lower files, as it also
+ * handles escaped whiteout files.
+ */
+bool ovl_path_is_whiteout(struct ovl_fs *ofs, const struct path *path)
+{
+ return ovl_is_whiteout(path->dentry) &&
+ !ovl_path_check_nowhiteout_xattr(ofs, path);
+}
+
struct file *ovl_path_open(const struct path *path, int flags)
{
struct inode *inode = d_inode(path->dentry);
@@ -663,6 +673,14 @@ void ovl_copy_up_end(struct dentry *dentry)
ovl_inode_unlock(d_inode(dentry));
}
+bool ovl_path_check_nowhiteout_xattr(struct ovl_fs *ofs, const struct path *path)
+{
+ int res;
+
+ res = ovl_path_getxattr(ofs, path, OVL_XATTR_NOWHITEOUT, NULL, 0);
+ return res >= 0;
+}
+
bool ovl_path_check_origin_xattr(struct ovl_fs *ofs, const struct path *path)
{
int res;
@@ -760,6 +778,7 @@ bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
#define OVL_XATTR_UUID_POSTFIX "uuid"
#define OVL_XATTR_METACOPY_POSTFIX "metacopy"
#define OVL_XATTR_PROTATTR_POSTFIX "protattr"
+#define OVL_XATTR_NOWHITEOUT_POSTFIX "nowhiteout"
#define OVL_XATTR_TAB_ENTRY(x) \
[x] = { [false] = OVL_XATTR_TRUSTED_PREFIX x ## _POSTFIX, \
@@ -775,6 +794,7 @@ const char *const ovl_xattr_table[][2] = {
OVL_XATTR_TAB_ENTRY(OVL_XATTR_UUID),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_METACOPY),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_PROTATTR),
+ OVL_XATTR_TAB_ENTRY(OVL_XATTR_NOWHITEOUT),
};
int ovl_check_setxattr(struct ovl_fs *ofs, struct dentry *upperdentry,
--
2.41.0
