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-rw-r--r--arch/x86/lib/usercopy.c103
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);