[PATCH 1/2] vfs: add file_dentry()

[PATCH 1/2] vfs: add file_dentry()

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@redhat.com>

Regular files opened on overlayfs will result in the file being opened on
the underlying filesystem, while f_path points to the overlayfs
mount/dentry.

This confuses filesystems which get the dentry from struct file and assume
it's theirs.

Add a new helper, file_dentry() [*], to get the filesystem's own dentry
from the file.  This simply compares file_inode(file->f_path.dentry) to
file_inode(file) and if they are equal returns file->f_path.dentry (this is
the common, non-overlayfs case).

In the uncommon case (regular file on overlayfs) it will call into
overlayfs's ->d_native_dentry() to get the underlying dentry matching
file_inode(file).

[*] If possible, it's better simply to use file_inode() instead.

Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Tested-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/open.c              |   11 +++++++++++
 fs/overlayfs/super.c   |   16 ++++++++++++++++
 include/linux/dcache.h |    1 +
 include/linux/fs.h     |    2 ++
 4 files changed, 30 insertions(+)

--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1234,6 +1234,8 @@ static inline struct inode *file_inode(c
 	return f->f_inode;
 }
 
+extern struct dentry *file_dentry(const struct file *file);
+
 static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
 {
 	return locks_lock_inode_wait(file_inode(filp), fl);
--- a/fs/open.c
+++ b/fs/open.c
@@ -831,6 +831,17 @@ char *file_path(struct file *filp, char
 }
 EXPORT_SYMBOL(file_path);
 
+struct dentry *file_dentry(const struct file *file)
+{
+	struct dentry *dentry = file->f_path.dentry;
+
+	if (likely(d_inode(dentry) == file_inode(file)))
+		return dentry;
+	else
+		return dentry->d_op->d_native_dentry(dentry, file_inode(file));
+}
+EXPORT_SYMBOL(file_dentry);
+
 /**
  * vfs_open - open the file at the given path
  * @path: path to open
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -336,14 +336,30 @@ static int ovl_dentry_weak_revalidate(st
 	return ret;
 }
 
+static struct dentry *ovl_d_native_dentry(struct dentry *dentry,
+					 struct inode *inode)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+	struct dentry *realentry = ovl_upperdentry_dereference(oe);
+
+	if (realentry && inode == d_inode(realentry))
+		return realentry;
+	realentry = __ovl_dentry_lower(oe);
+	if (realentry && inode == d_inode(realentry))
+		return realentry;
+	BUG();
+}
+
 static const struct dentry_operations ovl_dentry_operations = {
 	.d_release = ovl_dentry_release,
 	.d_select_inode = ovl_d_select_inode,
+	.d_native_dentry = ovl_d_native_dentry,
 };
 
 static const struct dentry_operations ovl_reval_dentry_operations = {
 	.d_release = ovl_dentry_release,
 	.d_select_inode = ovl_d_select_inode,
+	.d_native_dentry = ovl_d_native_dentry,
 	.d_revalidate = ovl_dentry_revalidate,
 	.d_weak_revalidate = ovl_dentry_weak_revalidate,
 };
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -161,6 +161,7 @@ struct dentry_operations {
 	struct vfsmount *(*d_automount)(struct path *);
 	int (*d_manage)(struct dentry *, bool);
 	struct inode *(*d_select_inode)(struct dentry *, unsigned);
+	struct dentry *(*d_native_dentry)(struct dentry *, struct inode *);
 } ____cacheline_aligned;
 
 /*

Re: [PATCH 1/2] vfs: add file_dentry()

[Trond Myklebust]

On Tue, Mar 8, 2016 at 10:47 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> From: Miklos Szeredi <mszeredi@redhat.com>
>
> Regular files opened on overlayfs will result in the file being opened on
> the underlying filesystem, while f_path points to the overlayfs
> mount/dentry.
>
> This confuses filesystems which get the dentry from struct file and assume
> it's theirs.
>
> Add a new helper, file_dentry() [*], to get the filesystem's own dentry
> from the file.  This simply compares file_inode(file->f_path.dentry) to
> file_inode(file) and if they are equal returns file->f_path.dentry (this is
> the common, non-overlayfs case).
>
> In the uncommon case (regular file on overlayfs) it will call into
> overlayfs's ->d_native_dentry() to get the underlying dentry matching
> file_inode(file).
>
> [*] If possible, it's better simply to use file_inode() instead.
>
> Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> Tested-by: Goldwyn Rodrigues <rgoldwyn@suse.com>

Reviewed-by: Trond Myklebust <trond.myklebust@primarydata.com>

> ---
>  fs/open.c              |   11 +++++++++++
>  fs/overlayfs/super.c   |   16 ++++++++++++++++
>  include/linux/dcache.h |    1 +
>  include/linux/fs.h     |    2 ++
>  4 files changed, 30 insertions(+)
>
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1234,6 +1234,8 @@ static inline struct inode *file_inode(c
>         return f->f_inode;
>  }
>
> +extern struct dentry *file_dentry(const struct file *file);
> +
>  static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
>  {
>         return locks_lock_inode_wait(file_inode(filp), fl);
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -831,6 +831,17 @@ char *file_path(struct file *filp, char
>  }
>  EXPORT_SYMBOL(file_path);
>
> +struct dentry *file_dentry(const struct file *file)
> +{
> +       struct dentry *dentry = file->f_path.dentry;
> +
> +       if (likely(d_inode(dentry) == file_inode(file)))
> +               return dentry;
> +       else
> +               return dentry->d_op->d_native_dentry(dentry, file_inode(file));
> +}
> +EXPORT_SYMBOL(file_dentry);
> +
>  /**
>   * vfs_open - open the file at the given path
>   * @path: path to open
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -336,14 +336,30 @@ static int ovl_dentry_weak_revalidate(st
>         return ret;
>  }
>
> +static struct dentry *ovl_d_native_dentry(struct dentry *dentry,
> +                                        struct inode *inode)
> +{
> +       struct ovl_entry *oe = dentry->d_fsdata;
> +       struct dentry *realentry = ovl_upperdentry_dereference(oe);
> +
> +       if (realentry && inode == d_inode(realentry))
> +               return realentry;
> +       realentry = __ovl_dentry_lower(oe);
> +       if (realentry && inode == d_inode(realentry))
> +               return realentry;
> +       BUG();
> +}
> +
>  static const struct dentry_operations ovl_dentry_operations = {
>         .d_release = ovl_dentry_release,
>         .d_select_inode = ovl_d_select_inode,
> +       .d_native_dentry = ovl_d_native_dentry,
>  };
>
>  static const struct dentry_operations ovl_reval_dentry_operations = {
>         .d_release = ovl_dentry_release,
>         .d_select_inode = ovl_d_select_inode,
> +       .d_native_dentry = ovl_d_native_dentry,
>         .d_revalidate = ovl_dentry_revalidate,
>         .d_weak_revalidate = ovl_dentry_weak_revalidate,
>  };
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -161,6 +161,7 @@ struct dentry_operations {
>         struct vfsmount *(*d_automount)(struct path *);
>         int (*d_manage)(struct dentry *, bool);
>         struct inode *(*d_select_inode)(struct dentry *, unsigned);
> +       struct dentry *(*d_native_dentry)(struct dentry *, struct inode *);
>  } ____cacheline_aligned;
>
>  /*

[PATCH 2/2] nfs: use file_dentry()

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@redhat.com>

NFS may be used as lower layer of overlayfs and accessing f_path.dentry can
lead to a crash.

Fix by replacing direct access of file->f_path.dentry with the
file_dentry() accessor, which will always return a native object.

Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Tested-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/nfs/dir.c      |    6 +++---
 fs/nfs/inode.c    |    2 +-
 fs/nfs/nfs4file.c |    4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -377,7 +377,7 @@ int nfs_readdir_xdr_filler(struct page *
  again:
 	timestamp = jiffies;
 	gencount = nfs_inc_attr_generation_counter();
-	error = NFS_PROTO(inode)->readdir(file->f_path.dentry, cred, entry->cookie, pages,
+	error = NFS_PROTO(inode)->readdir(file_dentry(file), cred, entry->cookie, pages,
 					  NFS_SERVER(inode)->dtsize, desc->plus);
 	if (error < 0) {
 		/* We requested READDIRPLUS, but the server doesn't grok it */
@@ -560,7 +560,7 @@ int nfs_readdir_page_filler(nfs_readdir_
 		count++;
 
 		if (desc->plus != 0)
-			nfs_prime_dcache(desc->file->f_path.dentry, entry);
+			nfs_prime_dcache(file_dentry(desc->file), entry);
 
 		status = nfs_readdir_add_to_array(entry, page);
 		if (status != 0)
@@ -864,7 +864,7 @@ static bool nfs_dir_mapping_need_revalid
  */
 static int nfs_readdir(struct file *file, struct dir_context *ctx)
 {
-	struct dentry	*dentry = file->f_path.dentry;
+	struct dentry	*dentry = file_dentry(file);
 	struct inode	*inode = d_inode(dentry);
 	nfs_readdir_descriptor_t my_desc,
 			*desc = &my_desc;
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -940,7 +940,7 @@ int nfs_open(struct inode *inode, struct
 {
 	struct nfs_open_context *ctx;
 
-	ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
+	ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode);
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 	nfs_file_set_open_context(filp, ctx);
--- a/fs/nfs/nfs4file.c
+++ b/fs/nfs/nfs4file.c
@@ -26,7 +26,7 @@ static int
 nfs4_file_open(struct inode *inode, struct file *filp)
 {
 	struct nfs_open_context *ctx;
-	struct dentry *dentry = filp->f_path.dentry;
+	struct dentry *dentry = file_dentry(filp);
 	struct dentry *parent = NULL;
 	struct inode *dir;
 	unsigned openflags = filp->f_flags;
@@ -57,7 +57,7 @@ nfs4_file_open(struct inode *inode, stru
 	parent = dget_parent(dentry);
 	dir = d_inode(parent);
 
-	ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
+	ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode);
 	err = PTR_ERR(ctx);
 	if (IS_ERR(ctx))
 		goto out;

Re: [PATCH 2/2] nfs: use file_dentry()

[Trond Myklebust]

On Tue, Mar 8, 2016 at 10:49 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> From: Miklos Szeredi <mszeredi@redhat.com>
>
> NFS may be used as lower layer of overlayfs and accessing f_path.dentry can
> lead to a crash.
>
> Fix by replacing direct access of file->f_path.dentry with the
> file_dentry() accessor, which will always return a native object.
>
> Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> Cc: Trond Myklebust <trond.myklebust@primarydata.com>
> Tested-by: Goldwyn Rodrigues <rgoldwyn@suse.com>

Acked-by: Trond Myklebust <trond.myklebust@primarydata.com>

> ---
>  fs/nfs/dir.c      |    6 +++---
>  fs/nfs/inode.c    |    2 +-
>  fs/nfs/nfs4file.c |    4 ++--
>  3 files changed, 6 insertions(+), 6 deletions(-)
>
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -377,7 +377,7 @@ int nfs_readdir_xdr_filler(struct page *
>   again:
>         timestamp = jiffies;
>         gencount = nfs_inc_attr_generation_counter();
> -       error = NFS_PROTO(inode)->readdir(file->f_path.dentry, cred, entry->cookie, pages,
> +       error = NFS_PROTO(inode)->readdir(file_dentry(file), cred, entry->cookie, pages,
>                                           NFS_SERVER(inode)->dtsize, desc->plus);
>         if (error < 0) {
>                 /* We requested READDIRPLUS, but the server doesn't grok it */
> @@ -560,7 +560,7 @@ int nfs_readdir_page_filler(nfs_readdir_
>                 count++;
>
>                 if (desc->plus != 0)
> -                       nfs_prime_dcache(desc->file->f_path.dentry, entry);
> +                       nfs_prime_dcache(file_dentry(desc->file), entry);
>
>                 status = nfs_readdir_add_to_array(entry, page);
>                 if (status != 0)
> @@ -864,7 +864,7 @@ static bool nfs_dir_mapping_need_revalid
>   */
>  static int nfs_readdir(struct file *file, struct dir_context *ctx)
>  {
> -       struct dentry   *dentry = file->f_path.dentry;
> +       struct dentry   *dentry = file_dentry(file);
>         struct inode    *inode = d_inode(dentry);
>         nfs_readdir_descriptor_t my_desc,
>                         *desc = &my_desc;
> --- a/fs/nfs/inode.c
> +++ b/fs/nfs/inode.c
> @@ -940,7 +940,7 @@ int nfs_open(struct inode *inode, struct
>  {
>         struct nfs_open_context *ctx;
>
> -       ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
> +       ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode);
>         if (IS_ERR(ctx))
>                 return PTR_ERR(ctx);
>         nfs_file_set_open_context(filp, ctx);
> --- a/fs/nfs/nfs4file.c
> +++ b/fs/nfs/nfs4file.c
> @@ -26,7 +26,7 @@ static int
>  nfs4_file_open(struct inode *inode, struct file *filp)
>  {
>         struct nfs_open_context *ctx;
> -       struct dentry *dentry = filp->f_path.dentry;
> +       struct dentry *dentry = file_dentry(filp);
>         struct dentry *parent = NULL;
>         struct inode *dir;
>         unsigned openflags = filp->f_flags;
> @@ -57,7 +57,7 @@ nfs4_file_open(struct inode *inode, stru
>         parent = dget_parent(dentry);
>         dir = d_inode(parent);
>
> -       ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
> +       ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode);
>         err = PTR_ERR(ctx);
>         if (IS_ERR(ctx))
>                 goto out;