Re: [PATCH net] ipv6: fix out-of-bound access in ip6_parse_tlv()

[Paolo Abeni <pabeni@redhat.com>]

On Wed, 2021-06-23 at 12:43 -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> First problem is that optlen is fetched without checking
> there is more than one byte to parse.
> 
> Fix this by taking care of IPV6_TLV_PAD1 before
> fetching optlen (under appropriate sanity checks against len)
> 
> Second problem is that IPV6_TLV_PADN checks of zero
> padding are performed before the check of remaining length.
> 
> Fixes: c1412fce7ecc ("net/ipv6/exthdrs.c: Strict PadN option checking")

Perhaps even:

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

for the first issue?

> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: Tom Herbert <tom@herbertland.com>
> ---
> 
> Only compiled, I would appreciate a solid review of this patch before merging it, thanks !
> 
>  net/ipv6/exthdrs.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> index 6f7da8f3e2e5849f917853984c69bf02a0f1e27c..007959d4d3748f1e21f83946024a9967d08b25b6 100644
> --- a/net/ipv6/exthdrs.c
> +++ b/net/ipv6/exthdrs.c
> @@ -135,18 +135,24 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
>  	len -= 2;
>  
>  	while (len > 0) {
> -		int optlen = nh[off + 1] + 2;
> -		int i;
> +		int optlen, i;
>  
> -		switch (nh[off]) {
> -		case IPV6_TLV_PAD1:
> +		if (nh[off] == IPV6_TLV_PAD1) {
>  			optlen = 1;

It looks like the above assignment is not needed anymore.

Other than that LGTM,

Thanks!

Paolo