From 8b4a2d50de67b746bcc472bd46c55d83eff668fc Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Sun, 18 Aug 2024 23:06:26 +0200
Subject: kernel: basic _sys_setxattr implementation

---
 src/kernel/syscalls.c    | 36 ++++++++++++++++++++++++++++++++++++
 src/kernel/vfs/request.c |  9 +++++++++
 src/kernel/vfs/request.h |  2 +-
 3 files changed, 46 insertions(+), 1 deletion(-)

(limited to 'src/kernel')

diff --git a/src/kernel/syscalls.c b/src/kernel/syscalls.c
index 436000c..50ff589 100644
--- a/src/kernel/syscalls.c
+++ b/src/kernel/syscalls.c
@@ -548,6 +548,41 @@ ssize_t _sys_getxattr(hid_t hid, const char __user *name, void __user *buf, size
 	return 0;
 }
 
+ssize_t _sys_setxattr(hid_t hid, const char __user *name, const void __user *buf, size_t len, int flags) {
+	Handle *h = hs_get(proc_cur->hs, hid);
+	if (!h) {
+		SYSCALL_RETURN(-EBADF);
+	}
+	if (h->type != HANDLE_FILE || flags != 0) {
+		SYSCALL_RETURN(-ENOSYS);
+	}
+	if (!h->writeable) {
+		SYSCALL_RETURN(-EACCES);
+	}
+	char tmpbuf[XATTRNAME_MAX];
+	size_t namelen = pcpy_from_str(proc_cur, tmpbuf, name, XATTRNAME_MAX);
+	if (namelen == 0) {
+		SYSCALL_RETURN(-EFAULT);
+	}
+	assert(namelen <= XATTRNAME_MAX);
+	assert(tmpbuf[namelen-1] == '\0');
+
+	char *namebuf = kmalloc(namelen, TagXattrName);
+	memcpy(namebuf, tmpbuf, namelen);
+
+	vfsreq_dispatchcopy((VfsReq) {
+		.type = VFSOP_SETXATTR,
+		.backend = h->backend,
+		.id = h->file_id,
+		.caller = proc_cur,
+		.kin = namebuf,
+		.kinlen = namelen-1,
+		.uin = buf,
+		.uinlen = len,
+	});
+	return 0;
+}
+
 long _sys_execbuf(void __user *ubuf, size_t len) {
 	if (len == 0) SYSCALL_RETURN(0);
 	static_assert(EXECBUF_MAX_LEN <= KMALLOC_MAX);
@@ -607,6 +642,7 @@ long _syscall(long num, long a, long b, long c, long d, long e) {
 		break; case _SYS_DUPLEX:	_sys_duplex(a, b, c);
 		break; case _SYS_INTR_RETURN:	_sys_intr_return((userptr_t)a, b);
 		break; case _SYS_GETXATTR:	_sys_getxattr(a, (userptr_t)b, (userptr_t)c, d, e);
+		break; case _SYS_SETXATTR:	_sys_setxattr(a, (userptr_t)b, (userptr_t)c, d, e);
 		break; case _SYS_EXECBUF:	_sys_execbuf((userptr_t)a, b);
 		break; case _SYS_DEBUG_KLOG:	_sys_debug_klog((userptr_t)a, b);
 		break;
diff --git a/src/kernel/vfs/request.c b/src/kernel/vfs/request.c
index 9c5b327..194ee49 100644
--- a/src/kernel/vfs/request.c
+++ b/src/kernel/vfs/request.c
@@ -174,6 +174,12 @@ vfsback_useraccept(VfsReq *req)
 			space -= len+1;
 		}
 		if (req->uin) {
+			if (space < req->uinlen && req->type == VFSOP_SETXATTR) {
+				/* don't truncate xattr values */
+				// TODO test
+				vfsreq_finish_short(req, -ERANGE);
+				return;
+			}
 			if (req->kin) {
 				/* save the address of the "second buffer" in id2,
 				 * which should be free */
@@ -181,6 +187,9 @@ vfsback_useraccept(VfsReq *req)
 				res.id2 = buf;
 			}
 
+			/* intentionally overriding the prior len */
+			assert(len == 0 || req->type == VFSOP_SETXATTR);
+
 			len = min(req->uinlen, space);
 			len = pcpy_bi(handler, buf, req->caller, req->uin, len);
 		}
diff --git a/src/kernel/vfs/request.h b/src/kernel/vfs/request.h
index 484fdd7..fa62b35 100644
--- a/src/kernel/vfs/request.h
+++ b/src/kernel/vfs/request.h
@@ -45,7 +45,7 @@ struct VfsReq {
 	size_t kinlen;
 
 	/* user inputs and outputs - just point to some buffer in the caller */
-	char __user *uin;
+	const char __user *uin;
 	size_t uinlen;
 	char __user *out;
 	size_t outlen;
-- 
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