s3: lib: nmblib. Clean up and harden nmb packet processing.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14239
OSS-FUZZ: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=20156
OSS-FUZZ: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=20157

Credit to oss-fuzz.
No security implications.

Signed-off-by: Jeremy Allison <jra@samba.org>
Pair programmed with: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Tue Jan 21 23:33:41 UTC 2020 on sn-devel-184

(cherry picked from commit ad236bb7590e423b4c69fe6028f2f3495977f48b)

diff --git a/source3/libsmb/nmblib.c b/source3/libsmb/nmblib.c
index 727939575a74895addd9667d2bbedba7dfdfb03a..0681450bae2ed3c74d040c217d270452a4d124ef 100644 (file)
--- a/source3/libsmb/nmblib.c
+++ b/source3/libsmb/nmblib.c
@@ -192,10 +192,14 @@ static int parse_nmb_name(char *inbuf,int ofs,int length, struct nmb_name *name)
 
        m = ubuf[offset];
 
-       if (!m)
-               return(0);
-       if ((m & 0xC0) || offset+m+2 > length)
-               return(0);
+       /* m must be 32 to exactly fill in the 16 bytes of the netbios name */
+       if (m != 32) {
+               return 0;
+       }
+       /* Cannot go past length. */
+       if (offset+m+2 > length) {
+               return 0;
+       }
 
        memset((char *)name,'\0',sizeof(*name));