asn1: additional sanity checking during BER decoding (CVE-2008-1673)

[backport of 2.6 commit ddb2c43594f22843e9f3153da151deaba1a834c5]

- Don't trust a length which is greater than the working buffer.
  An invalid length could cause overflow when calculating buffer size
  for decoding oid.

- An oid length of zero is invalid and allows for an off-by-one error when
  decoding oid because the first subid actually encodes first 2 subids.

- A primitive encoding may not have an indefinite length.

Thanks to Wei Wang from McAfee for report.

Cc: Steven French <sfrench@us.ibm.com>
Cc: stable@kernel.org
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[w@1wt.eu: backported to 2.4 : no cifs ; snmp in ip_nat_snmp_basic.c]
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/net/ipv4/netfilter/ip_nat_snmp_basic.c b/net/ipv4/netfilter/ip_nat_snmp_basic.c
index efc651c..87d71d4 100644 (file)
--- a/net/ipv4/netfilter/ip_nat_snmp_basic.c
+++ b/net/ipv4/netfilter/ip_nat_snmp_basic.c
@@ -232,6 +232,11 @@ static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
                        }
                }
        }
+
+       /* don't trust len bigger than ctx buffer */
+       if (*len > ctx->end - ctx->pointer)
+               return 0;
+
        return 1;
 }
 
@@ -248,7 +253,11 @@ static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
                
        if (!asn1_length_decode(ctx, &def, &len))
                return 0;
-               
+
+       /* primitive shall be definite, indefinite shall be constructed */
+       if (*con == ASN1_PRI && !def)
+               return 0;
+
        if (def)
                *eoc = ctx->pointer + len;
        else
@@ -433,6 +442,11 @@ static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
        unsigned long *optr;
        
        size = eoc - ctx->pointer + 1;
+
+       /* first subid actually encodes first two subids */
+       if (size < 2 || size > ULONG_MAX/sizeof(unsigned long))
+               return 0;
+
        *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
        if (*oid == NULL) {
                if (net_ratelimit())