[PATCH] strndup_user()
This patch series creates a strndup_user() function to easy copying C strings
from userspace. Also we avoid common pitfalls like userspace modifying the
final \0 after the strlen_user().
Signed-off-by: Davi Arnaut <davi.arnaut@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/string.h b/include/linux/string.h
index 369be32..dee2214 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -18,6 +18,8 @@
extern __kernel_size_t strspn(const char *,const char *);
extern __kernel_size_t strcspn(const char *,const char *);
+extern char *strndup_user(const char __user *, long);
+
/*
* Include machine specific inline routines
*/
diff --git a/mm/util.c b/mm/util.c
index 5f4bb59..49e29f7 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1,6 +1,8 @@
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/module.h>
+#include <linux/err.h>
+#include <asm/uaccess.h>
/**
* kzalloc - allocate memory. The memory is set to zero.
@@ -37,3 +39,38 @@
return buf;
}
EXPORT_SYMBOL(kstrdup);
+
+/*
+ * strndup_user - duplicate an existing string from user space
+ *
+ * @s: The string to duplicate
+ * @n: Maximum number of bytes to copy, including the trailing NUL.
+ */
+char *strndup_user(const char __user *s, long n)
+{
+ char *p;
+ long length;
+
+ length = strnlen_user(s, n);
+
+ if (!length)
+ return ERR_PTR(-EFAULT);
+
+ if (length > n)
+ return ERR_PTR(-EINVAL);
+
+ p = kmalloc(length, GFP_KERNEL);
+
+ if (!p)
+ return ERR_PTR(-ENOMEM);
+
+ if (copy_from_user(p, s, length)) {
+ kfree(p);
+ return ERR_PTR(-EFAULT);
+ }
+
+ p[length - 1] = '\0';
+
+ return p;
+}
+EXPORT_SYMBOL(strndup_user);