Re: [PATCH] btrfs: prevent potential out of bounds in btrfs_ioctl_snap_create_v2()

From: David Sterba <dsterba@suse.cz>
To: Dan Carpenter <dancarpenter@oracle.com>
Cc: Chris Mason <clm@fb.com>, Arne Jansen <sensille@gmx.net>,
	Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>,
	linux-btrfs@vger.kernel.org, kernel-janitors@vger.kernel.org
Subject: Re: [PATCH] btrfs: prevent potential out of bounds in btrfs_ioctl_snap_create_v2()
Date: Mon, 22 Feb 2021 20:33:03 +0100	[thread overview]
Message-ID: <20210222193302.GT1993@suse.cz> (raw)
In-Reply-To: <YCyx8u40HaplP7a+@mwanda>

On Wed, Feb 17, 2021 at 09:04:34AM +0300, Dan Carpenter wrote:
> The problem is we're copying "inherit" from user space but we don't
> necessarily know that we're copying enough data for a 64 byte
> struct.  Then the next problem is that "inherit" has a variable size
> array at the end, and we have to verify that array is the size we
> expected.
> 
> Fixes: 6f72c7e20dba: ("Btrfs: add qgroup inheritance")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> Presumably only root can create snapshots.

Well, no. After first analysis there are some "interesting memory access
patterns" possible, with a crafted data in the inherit member.

> Anyway, I have not tested
> this fix.  I believe it is correct, of course.  But perhaps it's best
> to check.

Yeah I'll write a test also to see where exactly the issues are. Thanks
for the report/fix.