From: Simon Ruderich <simon@ruderich.org>
Date: Sat, 1 Nov 2025 09:23:41 +0000 (+0100)
Subject: remote: guard against (very unlikely) truncation when reading symlink target
X-Git-Url: https://ruderich.org/simon/gitweb/?a=commitdiff_plain;h=975710f1451df0139ec444e471d384ca34361d97;p=safcm%2Fsafcm.git

remote: guard against (very unlikely) truncation when reading symlink target
---

diff --git a/remote/sync/files.go b/remote/sync/files.go
index 3f0f196..4ccca5d 100644
--- a/remote/sync/files.go
+++ b/remote/sync/files.go
@@ -264,10 +264,16 @@ reopen:
 			}
 			oldData = x
 		case fs.ModeSymlink:
-			buf := make([]byte, unix.PathMax)
+			buf := make([]byte, unix.PathMax+1)
 			n, err := unix.Readlinkat(parentFd, baseName, buf)
 			if err != nil {
-				return fmt.Errorf("reading old content: %v", err)
+				return fmt.Errorf("reading old target: %v", err)
+			}
+			if n == len(buf) {
+				// Cannot differentiate between exact match and truncation.
+				// This shouldn't occur with unix.PathMax but let's be
+				// careful.
+				return fmt.Errorf("old path possibly truncated")
 			}
 			oldData = buf[:n]
 		}