1 files changed, 103 insertions, 0 deletions

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index 97be9cb54483..d6ae30bbd7bb 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -7,6 +7,8 @@
 #include <linux/highmem.h>
 #include <linux/module.h>
 
+#include <asm/word-at-a-time.h>
+
 /*
  * best effort, GUP based copy_from_user() that is NMI-safe
  */
@@ -41,3 +43,104 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
         return len;
 }
 EXPORT_SYMBOL_GPL(copy_from_user_nmi);
+
+static inline unsigned long count_bytes(unsigned long mask)
+{
+        mask = (mask - 1) & ~mask;
+        mask >>= 7;
+        return count_masked_bytes(mask);
+}
+
+/*
+ * Do a strncpy, return length of string without final '\0'.
+ * 'count' is the user-supplied count (return 'count' if we
+ * hit it), 'max' is the address space maximum (and we return
+ * -EFAULT if we hit it).
+ */
+static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
+{
+        long res = 0;
+
+        /*
+         * Truncate 'max' to the user-specified limit, so that
+         * we only have one limit we need to check in the loop
+         */
+        if (max > count)
+                max = count;
+
+        while (max >= sizeof(unsigned long)) {
+                unsigned long c;
+
+                /* Fall back to byte-at-a-time if we get a page fault */
+                if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
+                        break;
+                /* This can write a few bytes past the NUL character, but that's ok */
+                *(unsigned long *)(dst+res) = c;
+                c = has_zero(c);
+                if (c)
+                        return res + count_bytes(c);
+                res += sizeof(unsigned long);
+                max -= sizeof(unsigned long);
+        }
+
+        while (max) {
+                char c;
+
+                if (unlikely(__get_user(c,src+res)))
+                        return -EFAULT;
+                dst[res] = c;
+                if (!c)
+                        return res;
+                res++;
+                max--;
+        }
+
+        /*
+         * Uhhuh. We hit 'max'. But was that the user-specified maximum
+         * too? If so, that's ok - we got as much as the user asked for.
+         */
+        if (res >= count)
+                return res;
+
+        /*
+         * Nope: we hit the address space limit, and we still had more
+         * characters the caller would have wanted. That's an EFAULT.
+         */
+        return -EFAULT;
+}
+
+/**
+ * strncpy_from_user: - Copy a NUL terminated string from userspace.
+ * @dst:   Destination address, in kernel space.  This buffer must be at
+ *         least @count bytes long.
+ * @src:   Source address, in user space.
+ * @count: Maximum number of bytes to copy, including the trailing NUL.
+ *
+ * Copies a NUL-terminated string from userspace to kernel space.
+ *
+ * On success, returns the length of the string (not including the trailing
+ * NUL).
+ *
+ * If access to userspace fails, returns -EFAULT (some data may have been
+ * copied).
+ *
+ * If @count is smaller than the length of the string, copies @count bytes
+ * and returns @count.
+ */
+long
+strncpy_from_user(char *dst, const char __user *src, long count)
+{
+        unsigned long max_addr, src_addr;
+
+        if (unlikely(count <= 0))
+                return 0;
+
+        max_addr = current_thread_info()->addr_limit.seg;
+        src_addr = (unsigned long)src;
+        if (likely(src_addr < max_addr)) {
+                unsigned long max = max_addr - src_addr;
+                return do_strncpy_from_user(dst, src, count, max);
+        }
+        return -EFAULT;
+}
+EXPORT_SYMBOL(strncpy_from_user);