From e6907e3a134df2f9a57a9e010f334fd3db50f32d Mon Sep 17 00:00:00 2001 From: Alessio Balsini Date: Mon, 25 Jan 2021 17:02:57 +0000 Subject: [PATCH] FROMLIST: fuse: Passthrough initialization and release Implement the FUSE passthrough ioctl that associates the lower (passthrough) file system file with the fuse_file. The file descriptor passed to the ioctl by the FUSE daemon is used to access the relative file pointer, that will be copied to the fuse_file data structure to consolidate the link between the FUSE and lower file system. To enable the passthrough mode, user space triggers the FUSE_DEV_IOC_PASSTHROUGH_OPEN ioctl and, if the call succeeds, receives back an identifier that will be used at open/create response time in the fuse_open_out field to associate the FUSE file to the lower file system file. The value returned by the ioctl to user space can be: - > 0: success, the identifier can be used as part of an open/create reply. - <= 0: an error occurred. The value 0 represents an error to preserve backward compatibility: the fuse_open_out field that is used to pass the passthrough_fh back to the kernel uses the same bits that were previously as struct padding, and is commonly zero-initialized (e.g., in the libfuse implementation). Removing 0 from the correct values fixes the ambiguity between the case in which 0 corresponds to a real passthrough_fh, a missing implementation of FUSE passthrough or a request for a normal FUSE file, simplifying the user space implementation. For the passthrough mode to be successfully activated, the lower file system file must implement both read_iter and write_iter file operations. This extra check avoids special pseudo files to be targeted for this feature. Passthrough comes with another limitation: no further file system stacking is allowed for those FUSE file systems using passthrough. Bug: 179164095 Link: https://lore.kernel.org/lkml/20210125153057.3623715-5-balsini@android.com/ Signed-off-by: Alessio Balsini Change-Id: I4d8290012302fb4547bce9bb261a03cc4f66b5aa Signed-off-by: Alessio Balsini --- fs/fuse/inode.c | 5 +++ fs/fuse/passthrough.c | 88 ++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 91 insertions(+), 2 deletions(-) diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c index ca68984f34cb..c5c261e77800 100755 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -983,6 +983,11 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req) static int free_fuse_passthrough(int id, void *p, void *data) { + struct fuse_passthrough *passthrough = (struct fuse_passthrough *)p; + + fuse_passthrough_release(passthrough); + kfree(p); + return 0; } diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c index 594060c654f8..b2a19e18a319 100644 --- a/fs/fuse/passthrough.c +++ b/fs/fuse/passthrough.c @@ -2,20 +2,104 @@ #include "fuse_i.h" +#include #include +#include int fuse_passthrough_open(struct fuse_dev *fud, struct fuse_passthrough_out *pto) { - return -EINVAL; + int res; + struct file *passthrough_filp; + struct fuse_conn *fc = fud->fc; + struct inode *passthrough_inode; + struct super_block *passthrough_sb; + struct fuse_passthrough *passthrough; + + if (!fc->passthrough) + return -EPERM; + + /* This field is reserved for future implementation */ + if (pto->len != 0) + return -EINVAL; + + passthrough_filp = fget(pto->fd); + if (!passthrough_filp) { + pr_err("FUSE: invalid file descriptor for passthrough.\n"); + return -EBADF; + } + + if (!passthrough_filp->f_op->read_iter || + !passthrough_filp->f_op->write_iter) { + pr_err("FUSE: passthrough file misses file operations.\n"); + res = -EBADF; + goto err_free_file; + } + + passthrough_inode = file_inode(passthrough_filp); + passthrough_sb = passthrough_inode->i_sb; + if (passthrough_sb->s_stack_depth >= FILESYSTEM_MAX_STACK_DEPTH) { + pr_err("FUSE: fs stacking depth exceeded for passthrough\n"); + res = -EINVAL; + goto err_free_file; + } + + passthrough = kmalloc(sizeof(struct fuse_passthrough), GFP_KERNEL); + if (!passthrough) { + res = -ENOMEM; + goto err_free_file; + } + + passthrough->filp = passthrough_filp; + + idr_preload(GFP_KERNEL); + spin_lock(&fc->passthrough_req_lock); + res = idr_alloc(&fc->passthrough_req, passthrough, 1, 0, GFP_ATOMIC); + spin_unlock(&fc->passthrough_req_lock); + idr_preload_end(); + + if (res > 0) + return res; + + fuse_passthrough_release(passthrough); + kfree(passthrough); + +err_free_file: + fput(passthrough_filp); + + return res; } int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff, struct fuse_open_out *openarg) { - return -EINVAL; + struct fuse_passthrough *passthrough; + int passthrough_fh = openarg->passthrough_fh; + + if (!fc->passthrough) + return -EPERM; + + /* Default case, passthrough is not requested */ + if (passthrough_fh <= 0) + return -EINVAL; + + spin_lock(&fc->passthrough_req_lock); + passthrough = idr_remove(&fc->passthrough_req, passthrough_fh); + spin_unlock(&fc->passthrough_req_lock); + + if (!passthrough) + return -EINVAL; + + ff->passthrough = *passthrough; + kfree(passthrough); + + return 0; } void fuse_passthrough_release(struct fuse_passthrough *passthrough) { + if (passthrough->filp) { + fput(passthrough->filp); + passthrough->filp = NULL; + } }