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

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

[Eric Dumazet]

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")
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;
 			padlen++;
 			if (padlen > 7)
 				goto bad;
-			break;
+			off++;
+			len--;
+			continue;
+		}
+		if (len < 2)
+			goto bad;
+		optlen = nh[off + 1] + 2;
+		if (optlen > len)
+			goto bad;
 
-		case IPV6_TLV_PADN:
+		if (nh[off] == IPV6_TLV_PADN) {
 			/* RFC 2460 states that the purpose of PadN is
 			 * to align the containing header to multiples
 			 * of 8. 7 is therefore the highest valid value.
@@ -163,12 +169,7 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
 				if (nh[off + i] != 0)
 					goto bad;
 			}
-			break;
-
-		default: /* Other TLV code so scan list */
-			if (optlen > len)
-				goto bad;
-
+		} else {
 			tlv_count++;
 			if (tlv_count > max_count)
 				goto bad;
@@ -188,7 +189,6 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
 				return false;
 
 			padlen = 0;
-			break;
 		}
 		off += optlen;
 		len -= optlen;
-- 
2.32.0.288.g62a8d224e6-goog

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

[Jakub Kicinski]

On Wed, 23 Jun 2021 12:43:53 -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")
> 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 !

Reviewed-by: Jakub Kicinski <kuba@kernel.org>

for what that's worth

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

[Paolo Abeni]

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

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

[Eric Dumazet]

On Thu, Jun 24, 2021 at 11:49 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> 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?
>

> +             if (nh[off] == IPV6_TLV_PAD1) {
> >                       optlen = 1;
>
> It looks like the above assignment is not needed anymore.
>
> Other than that LGTM,
>

Thanks for the review, I am sending the v2.