lib: Sparc's strncpy_from_user is generic enough, move under lib/
To use this, an architecture simply needs to:
1) Provide a user_addr_max() implementation via asm/uaccess.h
2) Add "select GENERIC_STRNCPY_FROM_USER" to their arch Kcnfig
3) Remove the existing strncpy_from_user() implementation and symbol
exports their architecture had.
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: David Howells <dhowells@redhat.com>
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
new file mode 100644
index 0000000..c4c09b0
--- /dev/null
+++ b/lib/strncpy_from_user.c
@@ -0,0 +1,146 @@
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+
+#include <asm/byteorder.h>
+
+static inline long find_zero(unsigned long mask)
+{
+ long byte = 0;
+
+#ifdef __BIG_ENDIAN
+#ifdef CONFIG_64BIT
+ if (mask >> 32)
+ mask >>= 32;
+ else
+ byte = 4;
+#endif
+ if (mask >> 16)
+ mask >>= 16;
+ else
+ byte += 2;
+ return (mask >> 8) ? byte : byte + 1;
+#else
+#ifdef CONFIG_64BIT
+ if (!((unsigned int) mask)) {
+ mask >>= 32;
+ byte = 4;
+ }
+#endif
+ if (!(mask & 0xffff)) {
+ mask >>= 16;
+ byte += 2;
+ }
+ return (mask & 0xff) ? byte : byte + 1;
+#endif
+}
+
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+#define IS_UNALIGNED(src, dst) 0
+#else
+#define IS_UNALIGNED(src, dst) \
+ (((long) dst | (long) src) & (sizeof(long) - 1))
+#endif
+
+/*
+ * 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)
+{
+ const unsigned long high_bits = REPEAT_BYTE(0xfe) + 1;
+ const unsigned long low_bits = REPEAT_BYTE(0x7f);
+ 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;
+
+ if (IS_UNALIGNED(src, dst))
+ goto byte_at_a_time;
+
+ while (max >= sizeof(unsigned long)) {
+ unsigned long c, v, rhs;
+
+ /* Fall back to byte-at-a-time if we get a page fault */
+ if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
+ break;
+ rhs = c | low_bits;
+ v = (c + high_bits) & ~rhs;
+ *(unsigned long *)(dst+res) = c;
+ if (v) {
+ v = (c & low_bits) + low_bits;
+ v = ~(v | rhs);
+ return res + find_zero(v);
+ }
+ res += sizeof(unsigned long);
+ max -= sizeof(unsigned long);
+ }
+
+byte_at_a_time:
+ 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 = user_addr_max();
+ 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);