fuzz:fuzz_conditional_ace_blob lets long generated SDDL fail

This can legitimately fail, due to e.g. integers being interpreted as
local attributes due to their position (the original data is complete
nonsense, bravely decompiled by sddl_from_conditional_ace).

In the example found the original begins like

00000000  61 72 74 78 02 00 00 00  00 00 00 00 00 03 01 02 |artx............|
00000010  f7 ff ff ff ff ff ff ff  03 01 a1 02 00 3b 00 00 |.............;..|
00000020  00 00 00 00 03 01 a1 02  00 3b 00 00 00 00 00 00 |.........;......|
00000030  03 01 02 a5 ff ff ff ff  ff ff ff 03 01 a1 02 78 |...............x|
00000040  00 00 00 00 00 00 00 03  01 85 02 00 3b 00 00 00 |............;...|
00000050  00 00 00 03 01 a1 02 00  3b 00 00 00 00 00 00 03 |........;.......|
00000060  01 02 a5 00 00 00 00 00  00 00 03 01 81 02 00 00 |................|
00000070  00 00 00 00 00 00 03 01  81 02 00 3b 00 00 00 00 |...........;....|

while the SDDL cycled version looks like

00000000  61 72 74 78 f8 04 00 00  00 30 00 30 00 f8 2e 00 |artx.....0.0....|
00000010  00 00 30 00 31 00 37 00  37 00 37 00 37 00 37 00 |..0.1.7.7.7.7.7.|
00000020  37 00 37 00 37 00 37 00  37 00 37 00 37 00 37 00 |7.7.7.7.7.7.7.7.|
00000030  37 00 37 00 37 00 37 00  37 00 37 00 36 00 37 00 |7.7.7.7.7.7.6.7.|
00000040  a1 f8 0c 00 00 00 30 00  33 00 35 00 34 00 30 00 |......0.3.5.4.0.|
00000050  30 00 a1 f8 0c 00 00 00  30 00 33 00 35 00 34 00 |0.......0.3.5.4.|
00000060  30 00 30 00 f8 2e 00 00  00 30 00 31 00 37 00 37 |0.0......0.1.7.7|
00000070  00 37 00 37 00 37 00 37  00 37 00 37 00 37 00 37 |.7.7.7.7.7.7.7.7|

and this new interpretation ends up being more than 10000 bytes long,
so the conversion fails.

The SDDL ends up looking like this:

  (((((((((((00) || (01777777777777777777767)) || (035400)) || \
  (((((((((((((((((((((((((((((((((((035400) || (01777777777777777777645)) \
  >= 0170) || (035400)) || (((((((((((((((((((((((((((((((035400 != 0245)
  [...]

where all the octal digits on the left hand side of operators are
UTF-16 strings.

REF: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=65322

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

diff --git a/lib/fuzzing/fuzz_conditional_ace_blob.c b/lib/fuzzing/fuzz_conditional_ace_blob.c
index ebbd90883aa8e8bec56f1831cb4dab5dabfabbe7..504ed2e14a1a94c1eabd6699104a0b906ac1a9ce 100644 (file)
--- a/lib/fuzzing/fuzz_conditional_ace_blob.c
+++ b/lib/fuzzing/fuzz_conditional_ace_blob.c
@@ -124,7 +124,18 @@ int LLVMFuzzerTestOneInput(const uint8_t *input, size_t len)
 
        ok = conditional_ace_encode_binary(mem_ctx, s2, &e2);
        if (! ok) {
-               abort();
+               if (len < CONDITIONAL_ACE_MAX_LENGTH / 4) {
+                       /*
+                        * long invalid ACEs can easily result in SDDL that
+                        * would compile to an over-long ACE, which fail
+                        * accordingly.
+                        *
+                        * But if the original ACE less than a few thousand
+                        * bytes, and it has been serialised into SDDL, that
+                        * SDDL should be parsable.
+                        */
+                       abort();
+               }
        }
 
        /*