From 24d464d38beb08cda1e972f79827d2fed6193de7 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Mon, 7 Mar 2022 16:30:44 +0100 Subject: [PATCH] BACKPORT: 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. Bug: 226679409 Reported-by: Jann Horn Fixes: c3021629a0d8 ("fuse: support splice() reading from fuse device") Cc: Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman Signed-off-by: Lee Jones Change-Id: I57a98e96e36bb97ce3e7b1ebf88917c6c8b0247d --- fs/fuse/dev.c | 12 +++++++++++- fs/fuse/file.c | 1 + fs/fuse/fuse_i.h | 1 + 3 files changed, 13 insertions(+), 1 deletion(-) diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index c93b0154dd51..e9a1543ba7cb 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -950,7 +950,17 @@ 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->args->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 97a40476d1bd..a68c8310942f 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -1420,6 +1420,7 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii, (PAGE_SIZE - ret) & (PAGE_SIZE - 1); } + ap->args.user_pages = true; if (write) ap->args.in_pages = true; else diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index fc5fcd8e0671..69a631c12b15 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -277,6 +277,7 @@ struct fuse_args { bool nocreds:1; bool in_pages:1; bool out_pages:1; + bool user_pages:1; bool out_argvar:1; bool page_zeroing:1; bool page_replace:1;