linux-kernel - Re: Patch "io_uring: reexpand under-reexpanded iters" has been added to the 5.13-stable tree

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Date:   Mon, 13 Sep 2021 12:47:50 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     asml.silence@...il.com, oswalpalash@...il.com,
        sudipm.mukherjee@...il.com,
        syzbot+9671693590ef5aad8953@...kaller.appspotmail.com,
        viro@...iv.linux.org.uk, stable-commits@...r.kernel.org
Subject: Re: Patch "io_uring: reexpand under-reexpanded iters" has been added
 to the 5.13-stable tree

On Mon, Sep 13, 2021 at 11:45:15AM +0200, gregkh@...uxfoundation.org wrote:
> 
> This is a note to let you know that I've just added the patch titled
> 
>     io_uring: reexpand under-reexpanded iters
> 
> to the 5.13-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      io_uring-reexpand-under-reexpanded-iters.patch
> and it can be found in the queue-5.13 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@...r.kernel.org> know about it.
> 
> 
> >From 89c2b3b74918200e46699338d7bcc19b1ea12110 Mon Sep 17 00:00:00 2001
> From: Pavel Begunkov <asml.silence@...il.com>
> Date: Mon, 23 Aug 2021 11:18:45 +0100
> Subject: io_uring: reexpand under-reexpanded iters
> 
> From: Pavel Begunkov <asml.silence@...il.com>
> 
> commit 89c2b3b74918200e46699338d7bcc19b1ea12110 upstream.
> 
> [   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@...r.kernel.org
> Reported-by: Palash Oswal <oswalpalash@...il.com>
> Reported-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>
> Reported-and-tested-by: syzbot+9671693590ef5aad8953@...kaller.appspotmail.com
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  fs/io_uring.c |    2 ++
>  1 file changed, 2 insertions(+)
> 

No, sorry, this breaks the build, now dropping.

greg k-h