From 29b721100aa5ad28a6c63ed79c9e4f0d30b8e333 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sun, 19 Oct 2025 13:05:04 -0400
Subject: kern: Add user creds with EUID and RUID + setuid()

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 src/sys/os/os_proc.c  |  8 ++++-
 src/sys/os/os_ucred.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+), 1 deletion(-)
 create mode 100644 src/sys/os/os_ucred.c

(limited to 'src/sys/os')

diff --git a/src/sys/os/os_proc.c b/src/sys/os/os_proc.c
index a8f49d7..ef6c04c 100644
--- a/src/sys/os/os_proc.c
+++ b/src/sys/os/os_proc.c
@@ -40,6 +40,7 @@
 #include <os/systm.h>
 #include <vm/vm.h>
 #include <vm/physseg.h>
+#include <os/ucred.h>
 #include <os/elfload.h>
 #include <os/signal.h>
 #include <os/kalloc.h>
@@ -386,9 +387,14 @@ proc_spawn(const char *path, struct penv_blk *envbp)
 
     proc->envblk = envbp;
     proc->parent = proc_self();
+    error = ucred_init(proc->parent, &proc->cred);
+    if (error < 0) {
+        kfree(proc);
+        return error;
+    }
+
     md_set_ip(proc, elf.entrypoint);
     sched_enq(&core->scq, proc);
-
     TAILQ_INSERT_TAIL(&procq, proc, lup_link);
     return proc->pid;
 }
diff --git a/src/sys/os/os_ucred.c b/src/sys/os/os_ucred.c
new file mode 100644
index 0000000..bf46308
--- /dev/null
+++ b/src/sys/os/os_ucred.c
@@ -0,0 +1,90 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the project nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <sys/cdefs.h>
+#include <sys/errno.h>
+#include <os/ucred.h>
+#include <os/ucred.h>
+
+int
+ucred_init(struct proc *proc, struct ucred *cred)
+{
+    struct ucred *curcred;
+
+    if (cred == NULL) {
+        return -EINVAL;
+    }
+
+    if (proc != NULL) {
+        curcred = &proc->cred;
+        cred->ruid = curcred->ruid;
+    } else {
+        cred->ruid = 0;
+    }
+
+    cred->euid = cred->ruid;
+    cred->suid = cred->ruid;
+    return 0;
+}
+
+int
+seteuid(uid_t euid)
+{
+    struct proc *self = proc_self();
+    struct ucred *cred;
+    int retval = -EPERM;
+
+    if (__unlikely(self == NULL)) {
+        return -ESRCH;
+    }
+
+    /* Verify against current creds */
+    cred = &self->cred;
+    if (euid == cred->euid || euid == cred->ruid) {
+        cred->euid = euid;
+        retval = 0;
+    } else if (euid == cred->suid || cred->euid == 0) {
+        cred->euid = euid;
+        retval = 0;
+    }
+
+    return retval;
+}
+
+/*
+ * ARG0: EUID
+ */
+scret_t
+sys_seteuid(struct syscall_args *scargs)
+{
+    uid_t euid = SCARG(scargs, int, 0);
+
+    return seteuid(euid);
+}
-- 
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