From bdb21a9f996a4eec2cceb6882875578ee6aa4034 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Mon, 7 Mar 2022 16:30:44 +0100 Subject: [PATCH] fuse: fix pipe buffer lifetime for direct_io commit 0c4bcfdecb1ac0967619ee7ff44871d93c08c909 upstream. In FOPEN_DIRECT_IO mode, fuse_file_write_iter() calls fuse_direct_write_iter(), which normally calls fuse_direct_io(), which then imports the write buffer with fuse_get_user_pages(), which uses iov_iter_get_pages() to grab references to userspace pages instead of actually copying memory. On the filesystem device side, these pages can then either be read to userspace (via fuse_dev_read()), or splice()d over into a pipe using fuse_dev_splice_read() as pipe buffers with &nosteal_pipe_buf_ops. This is wrong because after fuse_dev_do_read() unlocks the FUSE request, the userspace filesystem can mark the request as completed, causing write() to return. At that point, the userspace filesystem should no longer have access to the pipe buffer. Fix by copying pages coming from the user address space to new pipe buffers. Reported-by: Jann Horn Fixes: c3021629a0d8 ("fuse: support splice() reading from fuse device") Cc: Signed-off-by: Miklos Szeredi Signed-off-by: Zach O'Keefe Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- fs/fuse/dev.c | 12 +++++++++++- fs/fuse/file.c | 1 + fs/fuse/fuse_i.h | 2 ++ 3 files changed, 14 insertions(+), 1 deletion(-) diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 86c4b63f795c..cb3b992f9fe5 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -996,7 +996,17 @@ static int fuse_copy_page(struct fuse_copy_state *cs, struct page **pagep, while (count) { if (cs->write && cs->pipebufs && page) { - return fuse_ref_page(cs, page, offset, count); + /* + * Can't control lifetime of pipe buffers, so always + * copy user pages. + */ + if (cs->req->user_pages) { + err = fuse_copy_fill(cs); + if (err) + return err; + } else { + return fuse_ref_page(cs, page, offset, count); + } } else if (!cs->len) { if (cs->move_pages && page && offset == 0 && count == PAGE_SIZE) { diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 5ab9a70e2367..84322766ca7d 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -1319,6 +1319,7 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii, (PAGE_SIZE - ret) & (PAGE_SIZE - 1); } + req->user_pages = true; if (write) req->in.argpages = 1; else diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index 95d7b8282dfc..16e2c055442e 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -310,6 +310,8 @@ struct fuse_req { /** refcount */ atomic_t count; + bool user_pages; + /** Unique ID for the interrupt request */ u64 intr_unique;