[PATCH 4.19 158/421] ipv6: fix out-of-bound access in ip6_parse_tlv()

Greg Kroah-Hartman
2021-07-19T16:17:45Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 624085a31c1ad6a80b1e53f686bf6ee92abbf6e8 ]

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: 1da177e4c3f4 ("Linux-2.6.12-rc2")
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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv6/exthdrs.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 68b8084da83a..fe2497ae4523 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -138,18 +138,23 @@ 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:
- optlen = 1;
+ if (nh[off] == IPV6_TLV_PAD1) {
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.
@@ -166,12 +171,7 @@ 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;
@@ -191,7 +191,6 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
return false;

padlen = 0;
- break;
}
off += optlen;
len -= optlen;
--
2.30.2