Hello,
On Mon, Aug 14 2023, Harald Anlauf via Gcc-patches wrote:
> Hi Martin,
>
> Am 14.08.23 um 19:39 schrieb Martin Jambor:
>> Hello,
>>
>> this patch addresses an issue uncovered by the undefined behavior
>> sanitizer. In function resolve_structure_cons in resolve.cc there is
>> a test starting with:
>>
>> if (cons->expr->ts.type == BT_CHARACTER && comp->ts.u.cl
>> && comp->ts.u.cl->length
>> && comp->ts.u.cl->length->expr_type == EXPR_CONSTANT
>>
>> and UBSAN complained of loads from comp->ts.u.cl->length->expr_type of
>> integer value 1818451807 which is outside of the value range expr_t
>> enum. If I understand the code correctly it the entire load was
>> unwanted because comp->ts.type in those cases is BT_CLASS and not
>> BT_CHARACTER. This patch simply adds a check to make sure it is only
>> accessed in those cases.
>>
>> I have verified that the UPBSAN failure goes away with this patch, it
>> also passes bootstrap and testing on x86_64-linux. OK for master?
>
> this looks good to me.
>
> Looking at that code block, there is a potential other UB a few lines
> below, where (hopefully integer) string lengths are to be passed to
> mpz_cmp.
>
> If the string length is ill-defined (e.g. non-integer), value.integer
> is undefined. We've seen this elsewhere, where on BE platforms that
> undefined value was interpreted as some large integer and giving
> failures on those platforms. One could similarly add the following
> checks here (on top of your patch):
Thank you very much for the approval and the improvement. I have
committed the following (after another round of testing).
Martin
Fortran: Avoid accessing gfc_charlen when not looking at BT_CHARACTER (PR
110677)
This patch addresses an issue uncovered by the undefined behavior
sanitizer. In function resolve_structure_cons in resolve.cc there is
a test starting with:
if (cons->expr->ts.type == BT_CHARACTER && comp->ts.u.cl
&& comp->ts.u.cl->length
&& comp->ts.u.cl->length->expr_type == EXPR_CONSTANT
and UBSAN complained of loads from comp->ts.u.cl->length->expr_type of
integer value 1818451807 which is outside of the value range expr_t
enum. If I understand the code correctly it the entire load was
unwanted because comp->ts.type in those cases is BT_CLASS and not
BT_CHARACTER. This patch simply adds a check to make sure it is only
accessed in those cases.
During review, Harald Anlauf noticed that length types also need to be
checked and so I added also checks that he suggested to the condition.
Co-authored-by: Harald Anlauf <[email protected]>
gcc/fortran/ChangeLog:
2023-08-14 Martin Jambor <[email protected]>
PR fortran/110677
* resolve.cc (resolve_structure_cons): Check comp->ts is character
type before accessing stuff through comp->ts.u.cl.
---
gcc/fortran/resolve.cc | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
index e7c8d919bef..f51674f7faa 100644
--- a/gcc/fortran/resolve.cc
+++ b/gcc/fortran/resolve.cc
@@ -1396,11 +1396,14 @@ resolve_structure_cons (gfc_expr *expr, int init)
the one of the structure, ensure this if the lengths are known at
compile time and when we are dealing with PARAMETER or structure
constructors. */
- if (cons->expr->ts.type == BT_CHARACTER && comp->ts.u.cl
- && comp->ts.u.cl->length
+ if (cons->expr->ts.type == BT_CHARACTER
+ && comp->ts.type == BT_CHARACTER
+ && comp->ts.u.cl && comp->ts.u.cl->length
&& comp->ts.u.cl->length->expr_type == EXPR_CONSTANT
&& cons->expr->ts.u.cl && cons->expr->ts.u.cl->length
&& cons->expr->ts.u.cl->length->expr_type == EXPR_CONSTANT
+ && cons->expr->ts.u.cl->length->ts.type == BT_INTEGER
+ && comp->ts.u.cl->length->ts.type == BT_INTEGER
&& mpz_cmp (cons->expr->ts.u.cl->length->value.integer,
comp->ts.u.cl->length->value.integer) != 0)
{
--
2.41.0
