asn1: additional sanity checking during BER decoding

- 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>

1 files changed, 14 insertions, 0 deletions

diff --git a/fs/cifs/asn1.c b/fs/cifs/asn1.c
index cb52cbbe45ff..f58e41d3ba48 100644
--- a/fs/cifs/asn1.c
+++ b/fs/cifs/asn1.c
@@ -186,6 +186,11 @@ 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;
 }
 
@@ -203,6 +208,10 @@ 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
@@ -389,6 +398,11 @@ 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;