FAILED: patch "[PATCH] io_uring: reexpand under-reexpanded iters" failed to apply to 5.14-stable tree

FAILED: patch "[PATCH] io_uring: reexpand under-reexpanded iters" failed to apply to 5.14-stable tree

[gregkh]

The patch below does not apply to the 5.14-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 89c2b3b74918200e46699338d7bcc19b1ea12110 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Mon, 23 Aug 2021 11:18:45 +0100
Subject: [PATCH] io_uring: reexpand under-reexpanded iters

[   74.211232] BUG: KASAN: stack-out-of-bounds in iov_iter_revert+0x809/0x900
[   74.212778] Read of size 8 at addr ffff888025dc78b8 by task
syz-executor.0/828
[   74.214756] CPU: 0 PID: 828 Comm: syz-executor.0 Not tainted
5.14.0-rc3-next-20210730 #1
[   74.216525] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[   74.219033] Call Trace:
[   74.219683]  dump_stack_lvl+0x8b/0xb3
[   74.220706]  print_address_description.constprop.0+0x1f/0x140
[   74.224226]  kasan_report.cold+0x7f/0x11b
[   74.226085]  iov_iter_revert+0x809/0x900
[   74.227960]  io_write+0x57d/0xe40
[   74.232647]  io_issue_sqe+0x4da/0x6a80
[   74.242578]  __io_queue_sqe+0x1ac/0xe60
[   74.245358]  io_submit_sqes+0x3f6e/0x76a0
[   74.248207]  __do_sys_io_uring_enter+0x90c/0x1a20
[   74.257167]  do_syscall_64+0x3b/0x90
[   74.257984]  entry_SYSCALL_64_after_hwframe+0x44/0xae

old_size = iov_iter_count();
...
iov_iter_revert(old_size - iov_iter_count());

If iov_iter_revert() is done base on the initial size as above, and the
iter is truncated and not reexpanded in the middle, it miscalculates
borders causing problems. This trace is due to no one reexpanding after
generic_write_checks().

Now iters store how many bytes has been truncated, so reexpand them to
the initial state right before reverting.

Cc: stable@vger.kernel.org
Reported-by: Palash Oswal <oswalpalash@gmail.com>
Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Reported-and-tested-by: syzbot+9671693590ef5aad8953@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index d94fb5835a20..71639d39caf9 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3281,6 +3281,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
 		if (req->flags & REQ_F_NOWAIT)
 			goto done;
 		/* some cases will consume bytes even on error returns */
+		iov_iter_reexpand(iter, iter->count + iter->truncated);
 		iov_iter_revert(iter, io_size - iov_iter_count(iter));
 		ret = 0;
 	} else if (ret == -EIOCBQUEUED) {
@@ -3420,6 +3421,7 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 	} else {
 copy_iov:
 		/* some cases will consume bytes even on error returns */
+		iov_iter_reexpand(iter, iter->count + iter->truncated);
 		iov_iter_revert(iter, io_size - iov_iter_count(iter));
 		ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
 		return ret ?: -EAGAIN;