From 1ce8bc6c2bb7dac0aedcb016c9f06a980d3c9282 Mon Sep 17 00:00:00 2001
From: Armaan Sandhu <armaan.sandhu0504@gmail.com>
Date: Mon, 2 Nov 2026 13:15:55 -0500
Subject: [PATCH 1/2] reject an empty entry in the -u list

an empty entry like the first one in "-u ,99999", or a lone "^", was parsed as UID 0, so lsof listed or excluded root's files. report an error instead.
---
 Makefile.am                        |  1 +
 src/arg.c                          | 11 +++++++++++
 tests/case-20-uid-empty-entry.bash | 19 +++++++++++++++++++
 3 files changed, 31 insertions(+)
 create mode 100755 tests/case-20-uid-empty-entry.bash

diff --git a/Makefile.am b/Makefile.am
index 75086ca3..058098f6 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -132,6 +132,7 @@ DIALECT_NEUTRAL_TESTS = tests/case-00-hello.bash \
 	tests/case-20-handle-missing-files.bash \
 	tests/case-20-offset-field.bash \
 	tests/case-20-repeat-count.bash \
+	tests/case-20-uid-empty-entry.bash \
 	tests/case-21-exit-Q-status.bash \
 	tests/case-22-empty-process-name.bash \
 	tests/case-23-multi-address-hostname.bash \
diff --git a/src/arg.c b/src/arg.c
index 9bb09b9f..da71fdc5 100644
--- a/src/arg.c
+++ b/src/arg.c
@@ -2063,6 +2063,17 @@ int enter_uid(struct lsof_context *ctx, /* context */
             s++;
         if (j)
             continue;
+        if (!lnml) {
+
+            /*
+             * An empty entry (e.g. from ",99" or "^") would otherwise be
+             * taken as UID 0.
+             */
+            (void)fprintf(stderr, "%s: empty -u UID or login name: ", Pn);
+            safestrprt(us, stderr, 1);
+            err = 1;
+            continue;
+        }
         if (nn) {
             lnm[lnml++] = '\0';
             if ((pw = getpwnam(lnm)) == NULL) {
diff --git a/tests/case-20-uid-empty-entry.bash b/tests/case-20-uid-empty-entry.bash
new file mode 100755
index 00000000..c67d9d8d
--- /dev/null
+++ b/tests/case-20-uid-empty-entry.bash
@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+# An empty entry in a -u list must not be taken as UID 0.
+source tests/common.bash
+
+{
+    for spec in ",99999" "^"; do
+        output=$($lsof -u "$spec" -F u 2>/dev/null)
+        status=$?
+        if echo "$output" | grep -q '^u0$'; then
+            echo "lsof -u $spec selected UID 0" >> $report
+            exit 1
+        fi
+        if [ $status -eq 0 ]; then
+            echo "lsof -u $spec should fail" >> $report
+            exit 1
+        fi
+    done
+    exit 0
+} > $report 2>&1

From 5a15d3156975eb8c88795ae4796075fa293bacfe Mon Sep 17 00:00:00 2001
From: Armaan Sandhu <armaan.sandhu0504@gmail.com>
Date: Mon, 2 Nov 2026 19:27:22 -0500
Subject: [PATCH 2/2] reject an empty -u list too

-u "" was accepted with no UIDs at all, so lsof just listed evrything, root's files included. treat it like a missing argument and report "no UIDs specified".
---
 src/arg.c                          | 2 +-
 tests/case-20-uid-empty-entry.bash | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/arg.c b/src/arg.c
index da71fdc5..2005051c 100644
--- a/src/arg.c
+++ b/src/arg.c
@@ -2019,7 +2019,7 @@ int enter_uid(struct lsof_context *ctx, /* context */
     char *s, *st;
     uid_t uid;
 
-    if (!us) {
+    if (!us || !*us) {
         (void)fprintf(stderr, "%s: no UIDs specified\n", Pn);
         return (1);
     }
diff --git a/tests/case-20-uid-empty-entry.bash b/tests/case-20-uid-empty-entry.bash
index c67d9d8d..0149cdcc 100755
--- a/tests/case-20-uid-empty-entry.bash
+++ b/tests/case-20-uid-empty-entry.bash
@@ -3,7 +3,7 @@
 source tests/common.bash
 
 {
-    for spec in ",99999" "^"; do
+    for spec in "" ",99999" "^"; do
         output=$($lsof -u "$spec" -F u 2>/dev/null)
         status=$?
         if echo "$output" | grep -q '^u0$'; then