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

diff --git a/source3/libsmb/nmblib.c b/source3/libsmb/nmblib.c
index b6dca800e9466167515414b561a59aaa03f5eee8..84cbb054b8eb4eec1688e406c06e74175c2b0131 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));