Re: [PATCH v5] fuse: Add support for passthrough read/write
From: Jann Horn <hidden>
Date: 2016-02-02 08:10:35
Also in:
linux-fsdevel, lkml
On Mon, Feb 01, 2016 at 10:56:27AM -0800, Nikhilesh Reddy wrote:
Add support for filesystem passthrough read/write of files when enabled in userspace through the option FUSE_PASSTHROUGH.
[...]
quoted hunk ↗ jump to hunk
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
[...]
+static ssize_t fuse_passthrough_read_write_iter(struct kiocb *iocb,
+ struct iov_iter *iter, int do_write)
+{
+ ssize_t ret_val;
+ struct fuse_file *ff;
+ struct file *fuse_file, *passthrough_filp;
+ struct inode *fuse_inode, *passthrough_inode;
+
+ ff = iocb->ki_filp->private_data;
+ fuse_file = iocb->ki_filp;
+ passthrough_filp = ff->passthrough_filp;
+
+ /* lock passthrough file to prevent it from being released */
+ get_file(passthrough_filp);
+ iocb->ki_filp = passthrough_filp;
+ fuse_inode = fuse_file->f_path.dentry->d_inode;
+ passthrough_inode = file_inode(passthrough_filp);
+
+ if (do_write) {
+ if (!passthrough_filp->f_op->write_iter)
+ return -EIO;
+ ret_val = passthrough_filp->f_op->write_iter(iocb, iter);Uh... how do you know at this point that the file is actually writable? Normally, e.g. vfs_write() will ensure that the file is writable, and e.g. generic_file_write_iter() won't check for writability as far as I can tell. This might allow someone to use the passthrough mechanism to overwrite a file he is only allowed to read, but not write, like /etc/passwd. Also, I think this might bypass mandatory locks, the security_file_permission hook (which seems like a bad idea anyway though), inotify/fsnotify and sb_start_write.
quoted hunk ↗ jump to hunk
+ + if (ret_val >= 0 || ret_val == -EIOCBQUEUED) { + fsstack_copy_inode_size(fuse_inode, passthrough_inode); + fsstack_copy_attr_times(fuse_inode, passthrough_inode); + } + } else { + if (!passthrough_filp->f_op->read_iter) + return -EIO; + ret_val = passthrough_filp->f_op->read_iter(iocb, iter); + if (ret_val >= 0 || ret_val == -EIOCBQUEUED) + fsstack_copy_attr_atime(fuse_inode, passthrough_inode); + } + + iocb->ki_filp = fuse_file; + + /* unlock passthrough file */ + fput(passthrough_filp); + + return ret_val; +} + +ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *to) +{ + return fuse_passthrough_read_write_iter(iocb, to, 0); +} + +ssize_t fuse_passthrough_write_iter(struct kiocb *iocb, struct iov_iter *from) +{ + return fuse_passthrough_read_write_iter(iocb, from, 1); +} + +void fuse_passthrough_release(struct fuse_file *ff) +{ + if (!(ff->passthrough_filp)) + return; + + /* Release the passthrough file. */ + fput(ff->passthrough_filp); + ff->passthrough_filp = NULL; +}diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index c9aca04..a08933a 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h@@ -250,6 +250,7 @@ struct fuse_file_lock { #define FUSE_ASYNC_DIO (1 << 15) #define FUSE_WRITEBACK_CACHE (1 << 16) #define FUSE_NO_OPEN_SUPPORT (1 << 17) +#define FUSE_PASSTHROUGH (1 << 18) /** * CUSE INIT request/reply flags@@ -480,7 +481,7 @@ struct fuse_create_in { struct fuse_open_out { uint64_t fh; uint32_t open_flags; - uint32_t padding; + int32_t passthrough_fd; }; struct fuse_release_in {-- 1.8.2.1 -- Thanks Nikhilesh Reddy Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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