From fb7bb95209e7c835ce7f8f64684df695a4a43184 Mon Sep 17 00:00:00 2001
From: Jim Huang <jserv@ccns.ncku.edu.tw>
Date: Thu, 18 Jun 2026 01:13:04 +0800
Subject: [PATCH] Fix trailing-slash mkdir under sysroot

proc_resolve_sysroot_create_path located the leaf separator with
strrchr on the resolved sysroot path. A guest path ending in a slash
made strrchr match that trailing slash, so the parent buffer collapsed
to the target itself. The parent-existence access() then failed and the
resolver wrongly fell back to the host literal path (or auto-created the
target as if it were its own parent), so mkdir("/dir/") reported ENOENT
or EEXIST instead of creating the directory in the sysroot.

Drop trailing slashes before splitting off the leaf so the check sees
the real parent. Guard all-slash guest paths ("/", "///") up front:
they name the root, which always exists and has no parent, and trimming
would otherwise walk strrchr into the sysroot prefix and trip the
containment check (ELOOP) on a multi-component sysroot.

Close #100
---
 src/syscall/proc-state.c          | 16 +++++++++++
 tests/test-sysroot-create-paths.c | 44 +++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/src/syscall/proc-state.c b/src/syscall/proc-state.c
index 81dc4e0..fdda07d 100644
--- a/src/syscall/proc-state.c
+++ b/src/syscall/proc-state.c
@@ -592,8 +592,24 @@ const char *proc_resolve_sysroot_create_path(const char *path,
         return NULL;
     }
 
+    /* An all-slash guest path ("/", "///") names the root, which always exists
+     * and has no parent to check; trimming it would walk strrchr into the
+     * sysroot prefix and trip the containment guard.
+     *
+     * Return buf as-is.
+     */
+    if (path[strspn(path, "/")] == '\0')
+        return buf;
+
     char parent[LINUX_PATH_MAX];
     str_copy_trunc(parent, buf, sizeof(parent));
+    /* Trailing slashes name the same directory (POSIX); drop them so the final
+     * separator splits off the leaf component rather than matching the trailing
+     * slash itself, which would leave the target as its own parent.
+     */
+    size_t plen = strlen(parent);
+    while (plen > 1 && parent[plen - 1] == '/')
+        parent[--plen] = '\0';
     char *slash = strrchr(parent, '/');
     if (!slash || slash == parent)
         return buf;
diff --git a/tests/test-sysroot-create-paths.c b/tests/test-sysroot-create-paths.c
index 3ff1082..3eb1596 100644
--- a/tests/test-sysroot-create-paths.c
+++ b/tests/test-sysroot-create-paths.c
@@ -6,8 +6,10 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <string.h>
+#include <sys/stat.h>
 #include <sys/xattr.h>
 #include <unistd.h>
 
@@ -57,6 +59,23 @@ int main(int argc, char **argv)
 
     printf("test-sysroot-create-paths: create-path routing tests\n");
 
+    TEST("root create path stays inside sysroot");
+    {
+        const char *roots[] = {"/", "///"};
+        bool ok = true;
+        for (size_t i = 0; i < sizeof(roots) / sizeof(roots[0]); i++) {
+            errno = 0;
+            if (mkdir(roots[i], 0777) == 0 || errno != EEXIST) {
+                ok = false;
+                break;
+            }
+        }
+        if (ok)
+            PASS();
+        else
+            FAIL("mkdir root path returned wrong result");
+    }
+
     TEST("/tmp create is redirected into sysroot");
     {
         if (write_file(guest_tmp_path, "tmp-redir\n") < 0) {
@@ -75,6 +94,31 @@ int main(int argc, char **argv)
         }
     }
 
+    TEST("trailing-slash mkdir resolves against the real parent");
+    {
+        /* Issue #100: a trailing slash made the parent-existence check split
+         * the target off itself, so the create wrongly fell back / returned
+         * EEXIST instead of creating the directory in the sysroot.
+         */
+        const char *parent = "/tmp/elfuse-trailing-slash";
+        const char *child = "/tmp/elfuse-trailing-slash/child/";
+        struct stat st;
+        rmdir("/tmp/elfuse-trailing-slash/child");
+        rmdir(parent);
+        if (mkdir(parent, 0777) < 0 && errno != EEXIST) {
+            FAIL("parent mkdir failed");
+        } else if (mkdir(child, 0777) < 0) {
+            FAIL("trailing-slash mkdir failed");
+        } else if (stat("/tmp/elfuse-trailing-slash/child", &st) < 0 ||
+                   !S_ISDIR(st.st_mode)) {
+            FAIL("trailing-slash target is not a directory");
+        } else {
+            rmdir("/tmp/elfuse-trailing-slash/child");
+            rmdir(parent);
+            PASS();
+        }
+    }
+
     TEST("non-sysroot absolute create falls back to host");
     {
         if (write_file(host_fallback_path, "host-fallback\n") < 0) {