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Message-ID: <nycvar.YSQ.7.76.1911041928030.30289@knanqh.ubzr>
Date: Mon, 4 Nov 2019 19:33:57 +0100 (CET)
From: Nicolas Pitre <nico@...xnic.net>
To: Or Cohen <orcohen@...oaltonetworks.com>
cc: Greg KH <gregkh@...uxfoundation.org>, jslaby@...e.com,
textshell@...uujin.de, Daniel Vetter <daniel.vetter@...ll.ch>,
sam@...nborg.org, mpatocka@...hat.com, ghalat@...hat.com,
linux-kernel@...r.kernel.org, jwilk@...lk.net,
Nadav Markus <nmarkus@...oaltonetworks.com>,
syzkaller@...glegroups.com
Subject: Re: Bug report - slab-out-of-bounds in vcs_scr_readw
On Mon, 4 Nov 2019, Or Cohen wrote:
> @gregkh@...uxfoundation.org @nico@...xnic.net - Thanks for the quick response.
> @gregkh@...uxfoundation.org - Regarding your question, I don't think
> the 1 byte buffer is related to the problem. ( it's just was there in
> the initial reproducer the fuzzer created, and I forgot to remove it
> while reducing code from the reproducer ).
I think I know what the problem is. I have no time to test it though.
Please try this (untested) patch. Also please try running the same test
code but with vcsa6 in addition to vcsu6 to be sure.
---------- >8
Subject: [PATCH] vcs: add missing validation on vcs_size() returned value
One usage instance didn't account for the fact that vcs_size() may
return a negative error code.
Signed-off-by: Nicolas Pitre <npitre@...libre.com>
diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index 1f042346e7..fa07d79027 100644
--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -474,6 +474,10 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
goto unlock_out;
size = vcs_size(inode);
+ if (size < 0) {
+ ret = size;
+ goto unlock_out;
+ }
ret = -EINVAL;
if (pos < 0 || pos > size)
goto unlock_out;
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