crypto/dso/dso_win32.c: fix win32_joiner buffer sizing for dir-only paths

win32_joiner() always emits a trailing '\' when file_split->dir
is present, even if file_split->file is NULL. The previous length
calculation only reserved that byte when file_split->file was also
non-NULL, which could cause a one-byte overflow.

Resolves: https://github.com/openssl/openssl/issues/31260
Fixes: cbecb3ac3763 "There's an ongoing project to bring some kind of path selection mechanism to the ENGINE framework.  This means there there are going to be new functionality for the DSO part, and ultimately some way of merging two file specifications together.
CLA: trivial

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Eugene Syromiatnikov <esyr@openssl.org>
MergeDate: Tue May 26 09:36:02 2026
(Merged from https://github.com/openssl/openssl/pull/31266)

diff --git a/crypto/dso/dso_win32.c b/crypto/dso/dso_win32.c
index 2a9014d1e8f1408099652353dd3d7278e509075c..78cc6493241421b632a89f0282ba128d9e1a3e47 100644 (file)
--- a/crypto/dso/dso_win32.c
+++ b/crypto/dso/dso_win32.c
@@ -321,7 +321,7 @@ static char *win32_joiner(DSO *dso, const struct file_st *file_split)
         len++; /* 1 for ending \ */
     }
     len += file_split->dirlen;
-    if (file_split->dir && file_split->file) {
+    if (file_split->dir) {
         len++; /* 1 for ending \ */
     }
     len += file_split->filelen;