From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 24 Mar 2022 15:10:06 +0000 (-0400)
Subject: Introduce wrapper lttng_copy_struct_from_user
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=148f58fe47175d56d610a4461ddeb79b7d766b29;p=lttng-modules.git

Introduce wrapper lttng_copy_struct_from_user

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I67e3d0249bbfdb5bc6e9d469119220a1fe3f03fd
---

diff --git a/include/wrapper/uaccess.h b/include/wrapper/uaccess.h
index 4ccb26a0..eb1e4b20 100644
--- a/include/wrapper/uaccess.h
+++ b/include/wrapper/uaccess.h
@@ -26,4 +26,88 @@
 
 #endif /* LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,0,0) */
 
+#if LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,4,0)
+static __always_inline __must_check int
+lttng_copy_struct_from_user(void *dst, size_t ksize, const void __user *src,
+		      size_t usize)
+{
+	return copy_struct_from_user(dst, ksize, src, usize);
+}
+#else /* LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,4,0) */
+/**
+ * lttng_check_zeroed_user: check if a userspace buffer only contains zero bytes
+ * @from: Source address, in userspace.
+ * @size: Size of buffer.
+ *
+ * This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for
+ * userspace addresses (and is more efficient because we don't care where the
+ * first non-zero byte is).
+ *
+ * Returns:
+ *  * 0: There were non-zero bytes present in the buffer.
+ *  * 1: The buffer was full of zero bytes.
+ *  * -EFAULT: access to userspace failed.
+ */
+int lttng_check_zeroed_user(const void __user *from, size_t size)
+{
+	unsigned long val;
+	uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
+	int ret;
+
+	if (unlikely(size == 0))
+		return 1;
+
+	from -= align;
+	size += align;
+
+	if (!lttng_access_ok(VERIFY_READ, from, size)
+		return -EFAULT;
+
+	ret = get_user(val, (unsigned long __user *) from);
+	if (ret)
+		return ret;
+	if (align)
+		val &= ~aligned_byte_mask(align);
+
+	while (size > sizeof(unsigned long)) {
+		if (unlikely(val))
+			goto done;
+
+		from += sizeof(unsigned long);
+		size -= sizeof(unsigned long);
+
+		ret = get_user(val, (unsigned long __user *) from);
+		if (ret)
+			return ret;
+	}
+
+	if (size < sizeof(unsigned long))
+		val &= aligned_byte_mask(size);
+
+done:
+	return (val == 0);
+}
+
+static __always_inline __must_check int
+lttng_copy_struct_from_user(void *dst, size_t ksize, const void __user *src,
+		      size_t usize)
+{
+	size_t size = min(ksize, usize);
+	size_t rest = max(ksize, usize) - size;
+
+	/* Deal with trailing bytes. */
+	if (usize < ksize) {
+		memset(dst + size, 0, rest);
+	} else if (usize > ksize) {
+		int ret = lttng_check_zeroed_user(src + size, rest);
+		if (ret <= 0)
+			return ret ?: -E2BIG;
+	}
+	/* Copy the interoperable parts of the struct. */
+	if (copy_from_user(dst, src, size))
+		return -EFAULT;
+	return 0;
+}
+#endif /* LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,4,0) */
+
 #endif /* _LTTNG_WRAPPER_UACCESS_H */