Subject: Re: [PATCH] keys, dns: Fix missing size check of V1 server-list header

From: Pengfei Xu <[email-masked]>
Date: Wed, 10 Jan 2024 19:06:24 +0800

On 2024-01-10 at 10:14:28 +0000, David Howells wrote:
> Pengfei Xu <[email-masked]> wrote:
> 
> >   Bisected info between v6.7-rc7(keyctl05 passed) and v6.7-rc8(keyctl05 failed)
> > is in attached.
> > 
> > keyctl05 failed in add_key with type "dns_resolver" syscall step tracked
> > by strace:
> > "
> > [pid 863107] add_key("dns_resolver", "desc", "\0\0\1\377\0", 5, KEY_SPEC_SESSION_KEYRING <unfinished ...>
> > [pid 863106] <... alarm resumed>)       = 30
> > [pid 863107] <... add_key resumed>)     = -1 EINVAL (Invalid argument)
> > "
> 
> It should fail as the payload is actually invalid.  The payload specifies a
> version 1 format - and that requires a 6-byte header.  The bug the patched
> fixes is that whilst there is a length check for the basic 3-byte header,
> there was no length check for the extended v1 header.

Thanks for description!

> 
> > After increased the dns_res_payload to 7 bytes(6 bytes was still failed),
> 
> The following doesn't work for you?
> 
> 	echo -n -e '\0\0\01\xff\0\0' | keyctl padd dns_resolver desc @p

I tried as follows, 6 bytes failed and 7 bytes passed:
"
# echo -n -e '\0\0\01\xff\0\0' | keyctl padd dns_resolver desc @p
add_key: Invalid argument
# echo -n -e '\0\0\01\xff\0\0\0' | keyctl padd dns_resolver desc @p
74678921
# uname -r
6.7.0-rc8
"

Thanks!

> David