From 2ed0dc34326af28cb4a6cf97b229f3a7300bae6e Mon Sep 17 00:00:00 2001
From: Levi Neely <lkn@darkstar.example.net>
Date: Tue, 3 Mar 2026 15:53:07 +0100
Subject: [PATCH] Fix integer overflow in fake fileid calculation

Replace INT64_MAX - (UINT64_MAX - taskid) with INT64_MIN + taskid.
Avoids signed/unsigned mixing and signed overflow (UB).

Fixes #252
---
 pclsync/pfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/pclsync/pfs.c b/pclsync/pfs.c
index fa8ce64..1466d27 100644
--- a/pclsync/pfs.c
+++ b/pclsync/pfs.c
@@ -1389,8 +1389,10 @@ static int pfs_open(const char *path, struct fuse_file_info *fi) {
 
     } else { /* cr->fileid==0 */
       psync_fstask_local_creat_t *lc;
+      int64_t fake_fileid;
       lc = pfs_task_creat_get_local(cr);
-      of = pfs_create_file(INT64_MAX - (UINT64_MAX - cr->taskid), 0,
+      fake_fileid = INT64_MIN + (int64_t)cr->taskid;
+      of = pfs_create_file(fake_fileid, 0,
                                 lc->datalen, 0, 1, 0,
                                 pfs_task_get_ref_locked(folder),
                                 fpath->name, PSYNC_CRYPTO_INVALID_ENCODER);