net: add a new sockptr_t type

Add a uptr_t type that can hold a pointer to either a user or kernel
memory region, and simply helpers to copy to and from it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/sockptr.h b/include/linux/sockptr.h
new file mode 100644 (file)
index 0000000..700856e
--- /dev/null
+++ b/include/linux/sockptr.h
@@ -0,0 +1,104 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2020 Christoph Hellwig.
+ *
+ * Support for "universal" pointers that can point to either kernel or userspace
+ * memory.
+ */
+#ifndef _LINUX_SOCKPTR_H
+#define _LINUX_SOCKPTR_H
+
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+
+typedef struct {
+       union {
+               void            *kernel;
+               void __user     *user;
+       };
+       bool            is_kernel : 1;
+} sockptr_t;
+
+static inline bool sockptr_is_kernel(sockptr_t sockptr)
+{
+       return sockptr.is_kernel;
+}
+
+static inline sockptr_t KERNEL_SOCKPTR(void *p)
+{
+       return (sockptr_t) { .kernel = p, .is_kernel = true };
+}
+
+static inline sockptr_t USER_SOCKPTR(void __user *p)
+{
+       return (sockptr_t) { .user = p };
+}
+
+static inline bool sockptr_is_null(sockptr_t sockptr)
+{
+       return !sockptr.user && !sockptr.kernel;
+}
+
+static inline int copy_from_sockptr(void *dst, sockptr_t src, size_t size)
+{
+       if (!sockptr_is_kernel(src))
+               return copy_from_user(dst, src.user, size);
+       memcpy(dst, src.kernel, size);
+       return 0;
+}
+
+static inline int copy_to_sockptr(sockptr_t dst, const void *src, size_t size)
+{
+       if (!sockptr_is_kernel(dst))
+               return copy_to_user(dst.user, src, size);
+       memcpy(dst.kernel, src, size);
+       return 0;
+}
+
+static inline void *memdup_sockptr(sockptr_t src, size_t len)
+{
+       void *p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN);
+
+       if (!p)
+               return ERR_PTR(-ENOMEM);
+       if (copy_from_sockptr(p, src, len)) {
+               kfree(p);
+               return ERR_PTR(-EFAULT);
+       }
+       return p;
+}
+
+static inline void *memdup_sockptr_nul(sockptr_t src, size_t len)
+{
+       char *p = kmalloc_track_caller(len + 1, GFP_KERNEL);
+
+       if (!p)
+               return ERR_PTR(-ENOMEM);
+       if (copy_from_sockptr(p, src, len)) {
+               kfree(p);
+               return ERR_PTR(-EFAULT);
+       }
+       p[len] = '\0';
+       return p;
+}
+
+static inline void sockptr_advance(sockptr_t sockptr, size_t len)
+{
+       if (sockptr_is_kernel(sockptr))
+               sockptr.kernel += len;
+       else
+               sockptr.user += len;
+}
+
+static inline long strncpy_from_sockptr(char *dst, sockptr_t src, size_t count)
+{
+       if (sockptr_is_kernel(src)) {
+               size_t len = min(strnlen(src.kernel, count - 1) + 1, count);
+
+               memcpy(dst, src.kernel, len);
+               return len;
+       }
+       return strncpy_from_user(dst, src.user, count);
+}
+
+#endif /* _LINUX_SOCKPTR_H */