From b8e8a2f2535482f850aa12808dee030f38bb8e3b Mon Sep 17 00:00:00 2001
From: Jake Wallin <jakewallin42@gmail.com>
Date: Thu, 15 Oct 2026 05:45:03 +0000
Subject: [PATCH] cksum: reject empty checksum filenames on WASI

---
 .../src/lib/features/checksum/validate.rs       | 11 ++++++++++-
 tests/by-util/test_b2sum.rs                     | 17 +++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/uucore/src/lib/features/checksum/validate.rs b/src/uucore/src/lib/features/checksum/validate.rs
index 3153f74451d..ee525a9b98e 100644
--- a/src/uucore/src/lib/features/checksum/validate.rs
+++ b/src/uucore/src/lib/features/checksum/validate.rs
@@ -595,7 +595,16 @@ fn get_file_to_check(
         let print_error = |err: io::Error| {
             show!(err.map_err_context(|| { locale_aware_shell_escape(filename) }));
         };
-        match File::open(filename) {
+        // WASI can resolve an empty path to a preopened directory.
+        let file = if filename.is_empty() {
+            Err(io::Error::new(
+                io::ErrorKind::NotFound,
+                translate!("error-file-not-found"),
+            ))
+        } else {
+            File::open(filename)
+        };
+        match file {
             Ok(f) => {
                 if f.metadata()
                     .map_err(|_| LineCheckError::CantOpenFile)?
diff --git a/tests/by-util/test_b2sum.rs b/tests/by-util/test_b2sum.rs
index 8d523c371f7..fa565b6d06c 100644
--- a/tests/by-util/test_b2sum.rs
+++ b/tests/by-util/test_b2sum.rs
@@ -190,6 +190,23 @@ fn test_check_status_reports_unusable_checksum_input() {
         .stderr_contains("'standard input': no properly formatted checksum lines found");
 }
 
+#[test]
+fn test_check_empty_filename() {
+    let digest = "786a02f742015903c6c6fd852552d272912f4740e15847618a86e217f71f5419d25e1031afee585313896444934eb04b903a685b1448b755d56f701afe9be2ce";
+
+    for line in [format!("{digest} \n"), format!(" {digest}\t\n")] {
+        new_ucmd!()
+            .arg("--check")
+            .pipe_in(line)
+            .fails_with_code(1)
+            .stdout_is("'': FAILED open or read\n")
+            .stderr_is(
+                "b2sum: '': No such file or directory\n\
+                 b2sum: WARNING: 1 listed file could not be read\n",
+            );
+    }
+}
+
 #[test]
 fn test_invalid_b2sum_length_option_not_multiple_of_8() {
     let scene = TestScenario::new(util_name!());