Overlayfs uses open_with_fake_path() to allocate internal kernel files,
with a "fake" path - whose f_path is not on the same fs as f_inode.
Allocate a container struct backing_file for those internal files, that
is used to hold the "fake" ovl path along with the real path.
backing_file_real_path() can be used to access the stored real path.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/file_table.c | 50 +++++++++++++++++++++++++++++++++++++++++++--
fs/internal.h | 5 +++--
fs/open.c | 46 ++++++++++++++++++++++++++++++-----------
fs/overlayfs/file.c | 4 ++--
include/linux/fs.h | 23 ++++++++++++++++-----
5 files changed, 105 insertions(+), 23 deletions(-)
diff --git a/fs/file_table.c b/fs/file_table.c
index 4bc713865212..34a832504369 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -44,18 +44,40 @@ static struct kmem_cache *filp_cachep __read_mostly;
static struct percpu_counter nr_files __cacheline_aligned_in_smp;
+/* Container for backing file with optional real path */
+struct backing_file {
+ struct file file;
+ struct path real_path;
+};
+
+static inline struct backing_file *backing_file(struct file *f)
+{
+ return container_of(f, struct backing_file, file);
+}
+
+struct path *backing_file_real_path(struct file *f)
+{
+ return &backing_file(f)->real_path;
+}
+EXPORT_SYMBOL_GPL(backing_file_real_path);
+
static void file_free_rcu(struct rcu_head *head)
{
struct file *f = container_of(head, struct file, f_rcuhead);
put_cred(f->f_cred);
- kmem_cache_free(filp_cachep, f);
+ if (unlikely(f->f_mode & FMODE_BACKING))
+ kfree(backing_file(f));
+ else
+ kmem_cache_free(filp_cachep, f);
}
static inline void file_free(struct file *f)
{
security_file_free(f);
- if (!(f->f_mode & FMODE_NOACCOUNT))
+ if (unlikely(f->f_mode & FMODE_BACKING))
+ path_put(backing_file_real_path(f));
+ else
percpu_counter_dec(&nr_files);
call_rcu(&f->f_rcuhead, file_free_rcu);
}
@@ -226,6 +248,30 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
return f;
}
+/*
+ * Variant of alloc_empty_file() that allocates a backing_file container
+ * and doesn't check and modify nr_files.
+ *
+ * This is only for kernel internal use, and the allocate file must not be
+ * installed into file tables or such.
+ */
+struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
+{
+ struct backing_file *ff;
+ int error;
+
+ ff = kzalloc(sizeof(struct backing_file), GFP_KERNEL);
+ if (unlikely(!ff))
+ return ERR_PTR(-ENOMEM);
+
+ error = init_file(&ff->file, flags, cred);
+ if (unlikely(error))
+ return ERR_PTR(error);
+
+ ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT;
+ return &ff->file;
+}
+
/**
* alloc_file - allocate and initialize a 'struct file'
*
diff --git a/fs/internal.h b/fs/internal.h
index bd3b2810a36b..9c31078e0d16 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -97,8 +97,9 @@ extern void chroot_fs_refs(const struct path *, const struct path *);
/*
* file_table.c
*/
-extern struct file *alloc_empty_file(int, const struct cred *);
-extern struct file *alloc_empty_file_noaccount(int, const struct cred *);
+struct file *alloc_empty_file(int flags, const struct cred *cred);
+struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred);
+struct file *alloc_empty_backing_file(int flags, const struct cred *cred);
static inline void put_file_access(struct file *file)
{
diff --git a/fs/open.c b/fs/open.c
index c5da2b3eb105..059d7024155a 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1152,23 +1152,45 @@ struct file *kernel_file_open(const struct path *path, int flags,
}
EXPORT_SYMBOL_GPL(kernel_file_open);
-struct file *open_with_fake_path(const struct path *path, int flags,
- struct inode *inode, const struct cred *cred)
+/**
+ * backing_file_open - open a backing file for kernel internal use
+ * @path: path of the file to open
+ * @flags: open flags
+ * @path: path of the backing file
+ * @cred: credentials for open
+ *
+ * Open a file whose f_inode != d_inode(f_path.dentry).
+ * the returned struct file is embedded inside a struct backing_file
+ * container which is used to store the @real_path of the inode.
+ * The @real_path can be accessed by backing_file_real_path() and the
+ * real dentry can be accessed with file_dentry().
+ * The kernel internal backing file is not accounted in nr_files.
+ * This is only for kernel internal use, and must not be installed into
+ * file tables or such.
+ */
+struct file *backing_file_open(const struct path *path, int flags,
+ const struct path *real_path,
+ const struct cred *cred)
{
- struct file *f = alloc_empty_file_noaccount(flags, cred);
- if (!IS_ERR(f)) {
- int error;
+ struct file *f;
+ int error;
- f->f_path = *path;
- error = do_dentry_open(f, inode, NULL);
- if (error) {
- fput(f);
- f = ERR_PTR(error);
- }
+ f = alloc_empty_backing_file(flags, cred);
+ if (IS_ERR(f))
+ return f;
+
+ f->f_path = *path;
+ path_get(real_path);
+ *backing_file_real_path(f) = *real_path;
+ error = do_dentry_open(f, d_inode(real_path->dentry), NULL);
+ if (error) {
+ fput(f);
+ f = ERR_PTR(error);
}
+
return f;
}
-EXPORT_SYMBOL(open_with_fake_path);
+EXPORT_SYMBOL_GPL(backing_file_open);
#define WILL_CREATE(flags) (flags & (O_CREAT | __O_TMPFILE))
#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC)
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 39737c2aaa84..c610ae35b0b9 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -61,8 +61,8 @@ static struct file *ovl_open_realfile(const struct file *file,
if (!inode_owner_or_capable(real_idmap, realinode))
flags &= ~O_NOATIME;
- realfile = open_with_fake_path(&file->f_path, flags, realinode,
- current_cred());
+ realfile = backing_file_open(&file->f_path, flags, realpath,
+ current_cred());
}
revert_creds(old_cred);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1f8486e773af..ecf85a46fb2a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -171,6 +171,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
/* File supports non-exclusive O_DIRECT writes from multiple threads */
#define FMODE_DIO_PARALLEL_WRITE ((__force fmode_t)0x1000000)
+/* File is embedded in backing_file object */
+#define FMODE_BACKING ((__force fmode_t)0x2000000)
+
/* File was opened by fanotify and shouldn't generate fanotify events */
#define FMODE_NONOTIFY ((__force fmode_t)0x4000000)
@@ -2352,11 +2355,21 @@ static inline struct file *file_open_root_mnt(struct vfsmount *mnt,
return file_open_root(&(struct path){.mnt = mnt, .dentry = mnt->mnt_root},
name, flags, mode);
}
-extern struct file * dentry_open(const struct path *, int, const struct cred *);
-extern struct file *dentry_create(const struct path *path, int flags,
- umode_t mode, const struct cred *cred);
-extern struct file * open_with_fake_path(const struct path *, int,
- struct inode*, const struct cred *);
+struct file *dentry_open(const struct path *path, int flags,
+ const struct cred *creds);
+struct file *dentry_create(const struct path *path, int flags, umode_t mode,
+ const struct cred *cred);
+struct file *backing_file_open(const struct path *path, int flags,
+ const struct path *real_path,
+ const struct cred *cred);
+struct path *backing_file_real_path(struct file *f);
+static inline const struct path *f_real_path(struct file *f)
+{
+ if (unlikely(f->f_mode & FMODE_BACKING))
+ return backing_file_real_path(f);
+ return &f->f_path;
+}
+
static inline struct file *file_clone_open(struct file *file)
{
return dentry_open(&file->f_path, file->f_flags, file->f_cred);
--
2.34.1
