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

- 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.

Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Adrian Bunk <bunk@kernel.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/fs/cifs/asn1.c b/fs/cifs/asn1.c
index 086ae8f4a207..dcafda8315c3 100644
--- a/fs/cifs/asn1.c
+++ b/fs/cifs/asn1.c
@@ -183,6 +183,11 @@ asn1_length_decode(struct asn1_ctx *ctx, unsigned int *def, unsigned int *len)
 			}
 		}
 	}
+
+	/* don't trust len bigger than ctx buffer */
+	if (*len > ctx->end - ctx->pointer)
+		return 0;
+
 	return 1;
 }
 
@@ -200,6 +205,10 @@ 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
@@ -386,6 +395,11 @@ 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) {
 		return 0;