Commit f658adee authored Feb 06, 2020 by Miklos Szeredi

fix up iter on short count in fuse_direct_io()



fuse_direct_io() can end up advancing the iterator by more than the amount
of data read or written.  This case is handled by the generic code if going
through ->direct_IO(), but not in the FOPEN_DIRECT_IO case.

Fix by reverting the extra bytes from the iterator in case of error or a
short count.

To test: install lxcfs, then the following testcase
  int fd = open("/var/lib/lxcfs/proc/uptime", O_RDONLY);
  sendfile(1, fd, NULL, 16777216);
  sendfile(1, fd, NULL, 16777216);
will spew WARN_ON() in iov_iter_pipe().

Reported-by: Peter Geis <pgwipeout@gmail.com>
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: 3c3db095 ("fuse: use iov_iter based generic splice helpers")
Cc: <stable@vger.kernel.org> # v5.1
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

parent d5226fa6

fs/fuse/file.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -1465,6 +1465,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv io, struct iov_iter iter,
		}
		ia = NULL;
		if (nres < 0) {
		iov_iter_revert(iter, nbytes);
		err = nres;
		break;
		}
		@@ -1473,8 +1474,10 @@ ssize_t fuse_direct_io(struct fuse_io_priv io, struct iov_iter iter,
		count -= nres;
		res += nres;
		pos += nres;
		if (nres != nbytes)
		if (nres != nbytes) {
		iov_iter_revert(iter, nbytes - nres);
		break;
		}
		if (count) {
		max_pages = iov_iter_npages(iter, fc->max_pages);
		ia = fuse_io_alloc(io, max_pages);

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