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Message-ID: <CAOQ4uxjOgWDqufLcabkkPcxvFcrehzoDuO0d6kdJZuoiRBKStw@mail.gmail.com>
Date: Sat, 20 May 2023 15:33:32 +0300
From: Amir Goldstein <amir73il@...il.com>
To: Andrea Righi <andrea.righi@...onical.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, linux-unionfs@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ovl: make consistent use of OVL_FS()
On Sat, May 20, 2023 at 3:20 PM Andrea Righi <andrea.righi@...onical.com> wrote:
>
> Always use OVL_FS() to retrieve the corresponding struct ovl_fs from a
I don't mind this cleanup, but...
> struct super_block and make sure that it is exclusively used with an
> overlayfs superblock (otherwise, trigger a BUG).
>
> Signed-off-by: Andrea Righi <andrea.righi@...onical.com>
> ---
> fs/overlayfs/copy_up.c | 2 +-
> fs/overlayfs/export.c | 10 +++++-----
> fs/overlayfs/inode.c | 8 ++++----
> fs/overlayfs/namei.c | 2 +-
> fs/overlayfs/ovl_entry.h | 4 ++++
> fs/overlayfs/super.c | 10 +++++-----
> fs/overlayfs/util.c | 18 +++++++++---------
> 7 files changed, 29 insertions(+), 25 deletions(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index f658cc8ea492..60aa615820e7 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -905,7 +905,7 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
> static bool ovl_need_meta_copy_up(struct dentry *dentry, umode_t mode,
> int flags)
> {
> - struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
>
> if (!ofs->config.metacopy)
> return false;
> diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
> index defd4e231ad2..f5f0ef8e3ce8 100644
> --- a/fs/overlayfs/export.c
> +++ b/fs/overlayfs/export.c
> @@ -182,7 +182,7 @@ static int ovl_connect_layer(struct dentry *dentry)
> */
> static int ovl_check_encode_origin(struct dentry *dentry)
> {
> - struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
>
> /* Upper file handle for pure upper */
> if (!ovl_dentry_lower(dentry))
> @@ -434,7 +434,7 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
> struct dentry *real,
> const struct ovl_layer *layer)
> {
> - struct ovl_fs *ofs = sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(sb);
> struct dentry *index = NULL;
> struct dentry *this = NULL;
> struct inode *inode;
> @@ -655,7 +655,7 @@ static struct dentry *ovl_get_dentry(struct super_block *sb,
> struct ovl_path *lowerpath,
> struct dentry *index)
> {
> - struct ovl_fs *ofs = sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(sb);
> const struct ovl_layer *layer = upper ? &ofs->layers[0] : lowerpath->layer;
> struct dentry *real = upper ?: (index ?: lowerpath->dentry);
>
> @@ -680,7 +680,7 @@ static struct dentry *ovl_get_dentry(struct super_block *sb,
> 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 ovl_fs *ofs = OVL_FS(sb);
> struct dentry *dentry;
> struct dentry *upper;
>
> @@ -700,7 +700,7 @@ static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
> static struct dentry *ovl_lower_fh_to_d(struct super_block *sb,
> struct ovl_fh *fh)
> {
> - struct ovl_fs *ofs = sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(sb);
> struct ovl_path origin = { };
> struct ovl_path *stack = &origin;
> struct dentry *dentry = NULL;
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 541cf3717fc2..c27823f6e7aa 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -334,7 +334,7 @@ static const char *ovl_get_link(struct dentry *dentry,
>
> bool ovl_is_private_xattr(struct super_block *sb, const char *name)
> {
> - struct ovl_fs *ofs = sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(sb);
>
> if (ofs->config.userxattr)
> return strncmp(name, OVL_XATTR_USER_PREFIX,
> @@ -689,7 +689,7 @@ int ovl_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
> int ovl_update_time(struct inode *inode, struct timespec64 *ts, int flags)
> {
> if (flags & S_ATIME) {
> - struct ovl_fs *ofs = inode->i_sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(inode->i_sb);
> struct path upperpath = {
> .mnt = ovl_upper_mnt(ofs),
> .dentry = ovl_upperdentry_dereference(OVL_I(inode)),
> @@ -952,7 +952,7 @@ static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
>
> static void ovl_next_ino(struct inode *inode)
> {
> - struct ovl_fs *ofs = inode->i_sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(inode->i_sb);
>
> inode->i_ino = atomic_long_inc_return(&ofs->last_ino);
> if (unlikely(!inode->i_ino))
> @@ -1284,7 +1284,7 @@ struct inode *ovl_get_trap_inode(struct super_block *sb, struct dentry *dir)
> static bool ovl_hash_bylower(struct super_block *sb, struct dentry *upper,
> struct dentry *lower, bool index)
> {
> - struct ovl_fs *ofs = sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(sb);
>
> /* No, if pure upper */
> if (!lower)
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index cfb3420b7df0..d0f196b85541 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -832,7 +832,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> {
> struct ovl_entry *oe;
> const struct cred *old_cred;
> - struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> + struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
> struct ovl_entry *poe = dentry->d_parent->d_fsdata;
> struct ovl_entry *roe = dentry->d_sb->s_root->d_fsdata;
> struct ovl_path *stack = NULL, *origin_path = NULL;
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index fd11fe6d6d45..b91b3694ae26 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -5,6 +5,8 @@
> * Copyright (C) 2016 Red Hat, Inc.
> */
>
> +#include <uapi/linux/magic.h>
> +
> struct ovl_config {
> char *lowerdir;
> char *upperdir;
> @@ -97,6 +99,8 @@ static inline struct mnt_idmap *ovl_upper_mnt_idmap(struct ovl_fs *ofs)
>
> static inline struct ovl_fs *OVL_FS(struct super_block *sb)
> {
> + /* Make sure OVL_FS() is always used with an overlayfs superblock */
> + BUG_ON(sb->s_magic != OVERLAYFS_SUPER_MAGIC);
1. Adding new BUG_ON to kernel code is not acceptable - if anything
you can add WARN_ON_ONCE()
2. If anything, you should check s_type == s_ovl_fs_type, not s_magic
3. It is very unclear to me that this check has that much value and OVL_FS()
macro is very commonly used inside internal helpers, so please add a
"why" to your patch - why do you think that it is desired and/or valuable
to fortify OVL_FS() like this?
Thanks,
Amir.
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