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Unverified Commit 06d2948e authored by Alessio Balsini's avatar Alessio Balsini Committed by Michael Bestas
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ANDROID: fuse/passthrough: API V2 with __u32 open argument 

The initial FUSE passthrough interface has the issue of introducing an
ioctl which receives as a parameter a data structure containing a
pointer. What happens is that, depending on the architecture, the size
of this struct might change, and especially for 32-bit userspace running
on 64-bit kernel, the size mismatch results into different a single
ioctl the behavior of which depends on the data that is passed (e.g.,
with an enum). This is just a poor ioctl design as mentioned by Arnd
Bergmann [1].

Introduce the new FUSE_PASSTHROUGH_OPEN ioctl which only gets the fd of
the lower file system, which is a fixed-size __u32, dropping the
confusing fuse_passthrough_out data structure.

[1] https://lore.kernel.org/lkml/CAK8P3a2K2FzPvqBYL9W=Yut58SFXyetXwU4Fz50G5O3TsS0pPQ@mail.gmail.com/



Bug: 175195837
Signed-off-by: default avatarAlessio Balsini <balsini@google.com>
Change-Id: I486d71cbe20f3c0c87544fa75da4e2704fe57c7c
parent 4b9a79bd

fs/fuse/dev.c

+2 −5
Original line number Diff line number Diff line
@@ -2268,7 +2268,6 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd, 
	int res;

	int oldfd;

	struct fuse_dev *fud = NULL;

	struct fuse_passthrough_out pto;



	if (_IOC_TYPE(cmd) != FUSE_DEV_IOC_MAGIC)

		return -EINVAL;
@@ -2301,13 +2300,11 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd, 
		break;

	case _IOC_NR(FUSE_DEV_IOC_PASSTHROUGH_OPEN):

		res = -EFAULT;

		if (!copy_from_user(&pto,

				    (struct fuse_passthrough_out __user *)arg,

				    sizeof(pto))) {

		if (!get_user(oldfd, (__u32 __user *)arg)) {

			res = -EINVAL;

			fud = fuse_get_dev(file);

			if (fud)

				res = fuse_passthrough_open(fud, &pto);

				res = fuse_passthrough_open(fud, oldfd);

		}

		break;

	default:

fs/fuse/fuse_i.h

+1 −2
Original line number Diff line number Diff line
@@ -1135,8 +1135,7 @@ u64 fuse_get_unique(struct fuse_iqueue *fiq); 
void fuse_free_conn(struct fuse_conn *fc);



/* passthrough.c */

int fuse_passthrough_open(struct fuse_dev *fud,

			  struct fuse_passthrough_out *pto);

int fuse_passthrough_open(struct fuse_dev *fud, u32 lower_fd);

int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff,

			   struct fuse_open_out *openarg);

void fuse_passthrough_release(struct fuse_passthrough *passthrough);

fs/fuse/passthrough.c

+2 −7
Original line number Diff line number Diff line
@@ -191,8 +191,7 @@ ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma) 
	return ret;

}



int fuse_passthrough_open(struct fuse_dev *fud,

			  struct fuse_passthrough_out *pto)

int fuse_passthrough_open(struct fuse_dev *fud, u32 lower_fd)

{

	int res;

	struct file *passthrough_filp;
@@ -204,11 +203,7 @@ int fuse_passthrough_open(struct fuse_dev *fud, 
	if (!fc->passthrough)

		return -EPERM;



	/* This field is reserved for future implementation */

	if (pto->len != 0)

		return -EINVAL;



	passthrough_filp = fget(pto->fd);

	passthrough_filp = fget(lower_fd);

	if (!passthrough_filp) {

		pr_err("FUSE: invalid file descriptor for passthrough.\n");

		return -EBADF;

include/uapi/linux/fuse.h

+3 −10
Original line number Diff line number Diff line
@@ -796,14 +796,6 @@ struct fuse_in_header { 
	uint32_t	padding;

};



/* fuse_passthrough_out for passthrough V1 */

struct fuse_passthrough_out {

	uint32_t	fd;

	/* For future implementation */

	uint32_t	len;

	void		*vec;

};



struct fuse_out_header {

	uint32_t	len;

	int32_t		error;
@@ -881,8 +873,9 @@ struct fuse_notify_retrieve_in { 
/* Device ioctls: */

#define FUSE_DEV_IOC_MAGIC		229

#define FUSE_DEV_IOC_CLONE		_IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t)

/* 127 is reserved for the V1 interface implementation in Android */

#define FUSE_DEV_IOC_PASSTHROUGH_OPEN	_IOW(FUSE_DEV_IOC_MAGIC, 127, struct fuse_passthrough_out)

/* 127 is reserved for the V1 interface implementation in Android (deprecated) */

/* 126 is reserved for the V2 interface implementation in Android */

#define FUSE_DEV_IOC_PASSTHROUGH_OPEN	_IOW(FUSE_DEV_IOC_MAGIC, 126, __u32)



struct fuse_lseek_in {

	uint64_t	fh;