[gcc r9-9262] d: Fix heap-buffer-overflow in checkModFileAlias [PR 99337]

[Iain Buclaw]

https://gcc.gnu.org/g:03d7b32e0ebf15047a97d3f27faf5771ecf79a03

commit r9-9262-g03d7b32e0ebf15047a97d3f27faf5771ecf79a03
Author: Iain Buclaw <ibuclaw@gdcproject.org>
Date:   Wed Mar 3 15:34:04 2021 +0100

    d: Fix heap-buffer-overflow in checkModFileAlias [PR 99337]
    
    The code wrongly assumed memcmp did not read past the mismatch.
    
    gcc/d/ChangeLog:
    
            PR d/99337
            * dmd/dmodule.c (checkModFileAlias): Don't read past buffer in
              comparison.
    
    (cherry picked from commit d6177870dd2696501e3b8d3930fd5549d4acaeae)

Diff:
---
 gcc/d/dmd/dmodule.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/d/dmd/dmodule.c b/gcc/d/dmd/dmodule.c
index 1f6fd9f10a6..2779f627b8d 100644
--- a/gcc/d/dmd/dmodule.c
+++ b/gcc/d/dmd/dmodule.c
@@ -202,7 +202,7 @@ static void checkModFileAlias(OutBuffer *buf, OutBuffer *dotmods,
         const char *m = (*ms)[j];
         const char *q = strchr(m, '=');
         assert(q);
-        if (dotmods->offset <= (size_t)(q - m) && memcmp(dotmods->peekString(), m, q - m) == 0)
+        if (dotmods->offset == (size_t)(q - m) && memcmp(dotmods->peekString(), m, q - m) == 0)
         {
             buf->reset();
             size_t qlen = strlen(q + 1);