linux-kernel - Re: [PATCH 4.4 11/41] KEYS: fix writing past end of user-supplied buffer in keyring

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Message-ID: <1508168854.22379.25.camel@codethink.co.uk>
Date:   Mon, 16 Oct 2017 16:47:34 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Eric Biggers <ebiggers@...gle.com>,
        David Howells <dhowells@...hat.com>
Cc:     stable@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.4 11/41] KEYS: fix writing past end of user-supplied
 buffer in keyring_read()

On Tue, 2017-10-03 at 14:21 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Eric Biggers <ebiggers@...gle.com>
> 
> commit e645016abc803dafc75e4b8f6e4118f088900ffb upstream.
> 
> Userspace can call keyctl_read() on a keyring to get the list of IDs of
> keys in the keyring.  But if the user-supplied buffer is too small, the
> kernel would write the full list anyway --- which will corrupt whatever
> userspace memory happened to be past the end of the buffer.  Fix it by
> only filling the space that is available.
[...]

trusted_read() has the same bug.

Also, the comment above keyctl_read_key() says "return the amount of
data that is available in the key, irrespective of how much we copied
into the buffer."  All the other implementations of key_type::read seem
to follow that, but this changes keyring_read() to return buflen in
case of a truncated read.

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.