Re: [PATCH v1 2/6] virtio console: Harden port adding

On Thu, Jan 19, 2023 at 10:13:18PM +0200, Alexander Shishkin wrote:

Greg Kroah-Hartman [off-list ref] writes:

quoted

Then you need to copy it out once, and then only deal with the local
copy.  Otherwise you have an incomplete snapshot.

Ok, would you be partial to something like this:

quoted

From 1bc9bb84004154376c2a0cf643d53257da6d1cd7 Mon Sep 17 00:00:00 2001

From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Date: Thu, 19 Jan 2023 21:59:02 +0200
Subject: [PATCH] virtio console: Keep a local copy of the control structure

When handling control messages, instead of peeking at the device memory
to obtain bits of the control structure, take a snapshot of it once and
use it instead, to prevent it from changing under us. This avoids races
between port id validation and control event decoding, which can lead
to, for example, a NULL dereference in port removal of a nonexistent
port.

The control structure is small enough (8 bytes) that it can be cached
directly on the stack.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Amit Shah <amit@kernel.org>
---
 drivers/char/virtio_console.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

Yes, this looks much better, thanks!

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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