FUSE server calls the FUSE_DEV_IOC_BACKING_OPEN ioctl with a backing file
descriptor. If the call succeeds, a backing file identifier is returned.
A later change will be using this backing file id in a reply to OPEN
request with the flag FOPEN_PASSTHROUGH to setup passthrough of file
operations on the open FUSE file to the backing file.
The FUSE server should call FUSE_DEV_IOC_BACKING_CLOSE ioctl to close the
backing file by its id.
This can be done at any time, but if an open reply with FOPEN_PASSTHROUGH
flag is still in progress, the open may fail if the backing file is
closed before the fuse file was opened.
Setting up backing files requires a server with CAP_SYS_ADMIN privileges.
For the backing file to be successfully setup, the backing file must
implement both read_iter and write_iter file operations.
The limitation on the level of filesystem stacking allowed for the
backing file is enforced before setting up the backing file.
Signed-off-by: Alessio Balsini <balsini@xxxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/fuse/dev.c | 41 ++++++++++++
fs/fuse/fuse_i.h | 10 +++
fs/fuse/inode.c | 5 ++
fs/fuse/passthrough.c | 135 ++++++++++++++++++++++++++++++++++++++
include/uapi/linux/fuse.h | 9 +++
5 files changed, 200 insertions(+)
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index eba68b57bd7c..b680787bd66d 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2283,6 +2283,41 @@ static long fuse_dev_ioctl_clone(struct file *file, __u32 __user *argp)
return res;
}
+static long fuse_dev_ioctl_backing_open(struct file *file,
+ struct fuse_backing_map __user *argp)
+{
+ struct fuse_dev *fud = fuse_get_dev(file);
+ struct fuse_backing_map map;
+
+ if (!fud)
+ return -EINVAL;
+
+ if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+ return -EOPNOTSUPP;
+
+ if (copy_from_user(&map, argp, sizeof(map)))
+ return -EFAULT;
+
+ return fuse_backing_open(fud->fc, &map);
+}
+
+static long fuse_dev_ioctl_backing_close(struct file *file, __u32 __user *argp)
+{
+ struct fuse_dev *fud = fuse_get_dev(file);
+ int backing_id;
+
+ if (!fud)
+ return -EINVAL;
+
+ if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+ return -EOPNOTSUPP;
+
+ if (get_user(backing_id, argp))
+ return -EFAULT;
+
+ return fuse_backing_close(fud->fc, backing_id);
+}
+
static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
@@ -2292,6 +2327,12 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
case FUSE_DEV_IOC_CLONE:
return fuse_dev_ioctl_clone(file, argp);
+ case FUSE_DEV_IOC_BACKING_OPEN:
+ return fuse_dev_ioctl_backing_open(file, argp);
+
+ case FUSE_DEV_IOC_BACKING_CLOSE:
+ return fuse_dev_ioctl_backing_close(file, argp);
+
default:
return -ENOTTY;
}
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index cae525147856..fb9ef02cbf45 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -79,6 +79,7 @@ struct fuse_submount_lookup {
/** Container for data related to mapping to backing file */
struct fuse_backing {
struct file *file;
+ struct cred *cred;
/** refcount */
refcount_t count;
@@ -897,6 +898,11 @@ struct fuse_conn {
/* New writepages go into this bucket */
struct fuse_sync_bucket __rcu *curr_bucket;
+
+#ifdef CONFIG_FUSE_PASSTHROUGH
+ /** IDR for backing files ids */
+ struct idr backing_files_map;
+#endif
};
/*
@@ -1414,5 +1420,9 @@ static inline struct fuse_backing *fuse_inode_backing_set(struct fuse_inode *fi,
struct fuse_backing *fuse_backing_get(struct fuse_backing *fb);
void fuse_backing_put(struct fuse_backing *fb);
+void fuse_backing_files_init(struct fuse_conn *fc);
+void fuse_backing_files_free(struct fuse_conn *fc);
+int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map);
+int fuse_backing_close(struct fuse_conn *fc, int backing_id);
#endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index c771bd3c1336..c26a84439934 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -930,6 +930,9 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
fc->max_pages = FUSE_DEFAULT_MAX_PAGES_PER_REQ;
fc->max_pages_limit = FUSE_MAX_MAX_PAGES;
+ if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+ fuse_backing_files_init(fc);
+
INIT_LIST_HEAD(&fc->mounts);
list_add(&fm->fc_entry, &fc->mounts);
fm->fc = fc;
@@ -1392,6 +1395,8 @@ EXPORT_SYMBOL_GPL(fuse_send_init);
void fuse_free_conn(struct fuse_conn *fc)
{
WARN_ON(!list_empty(&fc->devices));
+ if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+ fuse_backing_files_free(fc);
kfree_rcu(fc, rcu);
}
EXPORT_SYMBOL_GPL(fuse_free_conn);
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index e8639c0a9ac6..6604d414adb5 100644
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -18,8 +18,11 @@ struct fuse_backing *fuse_backing_get(struct fuse_backing *fb)
static void fuse_backing_free(struct fuse_backing *fb)
{
+ pr_debug("%s: fb=0x%p\n", __func__, fb);
+
if (fb->file)
fput(fb->file);
+ put_cred(fb->cred);
kfree_rcu(fb, rcu);
}
@@ -28,3 +31,135 @@ void fuse_backing_put(struct fuse_backing *fb)
if (fb && refcount_dec_and_test(&fb->count))
fuse_backing_free(fb);
}
+
+void fuse_backing_files_init(struct fuse_conn *fc)
+{
+ idr_init(&fc->backing_files_map);
+}
+
+static int fuse_backing_id_alloc(struct fuse_conn *fc, struct fuse_backing *fb)
+{
+ int id;
+
+ idr_preload(GFP_KERNEL);
+ spin_lock(&fc->lock);
+ id = idr_alloc_cyclic(&fc->backing_files_map, fb, 1, 0, GFP_ATOMIC);
+ spin_unlock(&fc->lock);
+ idr_preload_end();
+
+ WARN_ON_ONCE(id == 0);
+ return id;
+}
+
+static struct fuse_backing *fuse_backing_id_remove(struct fuse_conn *fc,
+ int id)
+{
+ struct fuse_backing *fb;
+
+ spin_lock(&fc->lock);
+ fb = idr_remove(&fc->backing_files_map, id);
+ spin_unlock(&fc->lock);
+
+ return fb;
+}
+
+static int fuse_backing_id_free(int id, void *p, void *data)
+{
+ struct fuse_backing *fb = p;
+
+ WARN_ON_ONCE(refcount_read(&fb->count) != 1);
+ fuse_backing_free(fb);
+ return 0;
+}
+
+void fuse_backing_files_free(struct fuse_conn *fc)
+{
+ idr_for_each(&fc->backing_files_map, fuse_backing_id_free, NULL);
+ idr_destroy(&fc->backing_files_map);
+}
+
+int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
+{
+ struct file *file;
+ struct super_block *backing_sb;
+ struct fuse_backing *fb = NULL;
+ int res;
+
+ pr_debug("%s: fd=%d flags=0x%x\n", __func__, map->fd, map->flags);
+
+ /* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
+ res = -EPERM;
+ if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
+ goto out;
+
+ res = -EINVAL;
+ if (map->flags)
+ goto out;
+
+ file = fget(map->fd);
+ res = -EBADF;
+ if (!file)
+ goto out;
+
+ res = -EOPNOTSUPP;
+ if (!file->f_op->read_iter || !file->f_op->write_iter)
+ goto out_fput;
+
+ backing_sb = file_inode(file)->i_sb;
+ res = -ELOOP;
+ if (backing_sb->s_stack_depth >= fc->max_stack_depth)
+ goto out_fput;
+
+ fb = kmalloc(sizeof(struct fuse_backing), GFP_KERNEL);
+ res = -ENOMEM;
+ if (!fb)
+ goto out_fput;
+
+ fb->file = file;
+ fb->cred = prepare_creds();
+ refcount_set(&fb->count, 1);
+
+ res = fuse_backing_id_alloc(fc, fb);
+ if (res < 0) {
+ fuse_backing_free(fb);
+ fb = NULL;
+ }
+
+out:
+ pr_debug("%s: fb=0x%p, ret=%i\n", __func__, fb, res);
+
+ return res;
+
+out_fput:
+ fput(file);
+ goto out;
+}
+
+int fuse_backing_close(struct fuse_conn *fc, int backing_id)
+{
+ struct fuse_backing *fb = NULL;
+ int err;
+
+ pr_debug("%s: backing_id=%d\n", __func__, backing_id);
+
+ /* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
+ err = -EPERM;
+ if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
+ goto out;
+
+ err = -EINVAL;
+ if (backing_id <= 0)
+ goto out;
+
+ err = -ENOENT;
+ fb = fuse_backing_id_remove(fc, backing_id);
+ if (!fb)
+ goto out;
+
+ fuse_backing_put(fb);
+ err = 0;
+out:
+ pr_debug("%s: fb=0x%p, err=%i\n", __func__, fb, err);
+
+ return err;
+}
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index edfc458e5e8f..af0fe3aec329 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -1059,9 +1059,18 @@ struct fuse_notify_retrieve_in {
uint64_t dummy4;
};
+struct fuse_backing_map {
+ int32_t fd;
+ uint32_t flags;
+ uint64_t padding;
+};
+
/* Device ioctls: */
#define FUSE_DEV_IOC_MAGIC 229
#define FUSE_DEV_IOC_CLONE _IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t)
+#define FUSE_DEV_IOC_BACKING_OPEN _IOW(FUSE_DEV_IOC_MAGIC, 1, \
+ struct fuse_backing_map)
+#define FUSE_DEV_IOC_BACKING_CLOSE _IOW(FUSE_DEV_IOC_MAGIC, 2, uint32_t)
struct fuse_lseek_in {
uint64_t fh;
--
2.34.1
