[SRU X] netlabel: cope with NULL catmap

[Thadeu Lima de Souza Cascardo]

From: Paolo Abeni <pabeni at redhat.com>

The cipso and calipso code can set the MLS_CAT attribute on
successful parsing, even if the corresponding catmap has
not been allocated, as per current configuration and external
input.

Later, selinux code tries to access the catmap if the MLS_CAT flag
is present via netlbl_catmap_getlong(). That may cause null ptr
dereference while processing incoming network traffic.

Address the issue setting the MLS_CAT flag only if the catmap is
really allocated. Additionally let netlbl_catmap_getlong() cope
with NULL catmap.

Reported-by: Matthew Sheets <matthew.sheets at gd-ms.com>
Fixes: 4b8feff251da ("netlabel: fix the horribly broken catmap functions")
Fixes: ceba1832b1b2 ("calipso: Set the calipso socket label to match the secattr.")
Signed-off-by: Paolo Abeni <pabeni at redhat.com>
Acked-by: Paul Moore <paul at paul-moore.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(backported from commit eead1c2ea2509fd754c6da893a94f0e69e83ebe4)
[cascardo: calipso code is not present]
CVE-2020-10711
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 net/ipv4/cipso_ipv4.c        | 6 ++++--
 net/netlabel/netlabel_kapi.c | 6 ++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 98ed5e43ab7b..0e83c5b08e0e 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -1343,7 +1343,8 @@ static int cipso_v4_parsetag_rbm(const struct cipso_v4_doi *doi_def,
 			return ret_val;
 		}
 
-		secattr->flags |= NETLBL_SECATTR_MLS_CAT;
+		if (secattr->attr.mls.cat)
+			secattr->flags |= NETLBL_SECATTR_MLS_CAT;
 	}
 
 	return 0;
@@ -1524,7 +1525,8 @@ static int cipso_v4_parsetag_rng(const struct cipso_v4_doi *doi_def,
 			return ret_val;
 		}
 
-		secattr->flags |= NETLBL_SECATTR_MLS_CAT;
+		if (secattr->attr.mls.cat)
+			secattr->flags |= NETLBL_SECATTR_MLS_CAT;
 	}
 
 	return 0;
diff --git a/net/netlabel/netlabel_kapi.c b/net/netlabel/netlabel_kapi.c
index bfa2b6d5b5cf..25ab12e25e05 100644
--- a/net/netlabel/netlabel_kapi.c
+++ b/net/netlabel/netlabel_kapi.c
@@ -605,6 +605,12 @@ int netlbl_catmap_getlong(struct netlbl_lsm_catmap *catmap,
 	if ((off & (BITS_PER_LONG - 1)) != 0)
 		return -EINVAL;
 
+	/* a null catmap is equivalent to an empty one */
+	if (!catmap) {
+		*offset = (u32)-1;
+		return 0;
+	}
+
 	if (off < catmap->startbit) {
 		off = catmap->startbit;
 		*offset = off;
-- 
2.25.1