1 files changed, 45 insertions, 54 deletions

diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index a28df5206d95..4a6574b67f82 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -1,16 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
 #include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/uaccess.h>
+#include <linux/mm.h>
+#include <linux/bitops.h>
 
 #include <asm/word-at-a-time.h>
 
-/* Set bits in the first 'n' bytes when loaded from memory */
-#ifdef __LITTLE_ENDIAN
-#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
-#else
-#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
-#endif
-
 /*
  * Do a strnlen, return length of string *with* final '\0'.
  * 'count' is the user-supplied count, while 'max' is the
@@ -24,29 +20,21 @@
  * if it fits in a aligned 'long'. The caller needs to check
  * the return value against "> max".
  */
-static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
+static __always_inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
 {
 	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
-	long align, res = 0;
+	unsigned long align, res = 0;
 	unsigned long c;
 
 	/*
-	 * 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;
-
-	/*
 	 * Do everything aligned. But that means that we
 	 * need to also expand the maximum..
 	 */
-	align = (sizeof(long) - 1) & (unsigned long)src;
+	align = (sizeof(unsigned long) - 1) & (unsigned long)src;
 	src -= align;
 	max += align;
 
-	if (unlikely(__get_user(c,(unsigned long __user *)src)))
-		return 0;
+	unsafe_get_user(c, (unsigned long __user *)src, efault);
 	c |= aligned_byte_mask(align);
 
 	for (;;) {
@@ -57,11 +45,11 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
 			return res + find_zero(data) + 1 - align;
 		}
 		res += sizeof(unsigned long);
-		if (unlikely(max < sizeof(unsigned long)))
+		/* We already handled 'unsigned long' bytes. Did we do it all ? */
+		if (unlikely(max <= sizeof(unsigned long)))
 			break;
 		max -= sizeof(unsigned long);
-		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
-			return 0;
+		unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
 	}
 	res -= align;
 
@@ -76,6 +64,7 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
 	 * Nope: we hit the address space limit, and we still had more
 	 * characters the caller would have wanted. That's 0.
 	 */
+efault:
 	return 0;
 }
 
@@ -84,13 +73,21 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
  * @str: The string to measure.
  * @count: Maximum count (including NUL character)
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are
+ *          enabled.
  *
  * Get the size of a NUL-terminated string in user space.
  *
  * Returns the size of the string INCLUDING the terminating NUL.
- * If the string is too long, returns 'count+1'.
+ * If the string is too long, returns a number larger than @count. User
+ * has to check the return value against "> count".
  * On exception (or invalid count), returns 0.
+ *
+ * NOTE! You should basically never use this function. There is
+ * almost never any valid case for using the length of a user space
+ * string, since the string can be changed at any time by other
+ * threads. Use "strncpy_from_user()" instead to get a stable copy
+ * of the string.
  */
 long strnlen_user(const char __user *str, long count)
 {
@@ -99,40 +96,34 @@ long strnlen_user(const char __user *str, long count)
 	if (unlikely(count <= 0))
 		return 0;
 
-	max_addr = user_addr_max();
-	src_addr = (unsigned long)str;
-	if (likely(src_addr < max_addr)) {
-		unsigned long max = max_addr - src_addr;
-		return do_strnlen_user(str, count, max);
-	}
-	return 0;
-}
-EXPORT_SYMBOL(strnlen_user);
+	if (can_do_masked_user_access()) {
+		long retval;
 
-/**
- * strlen_user: - Get the size of a user string INCLUDING final NUL.
- * @str: The string to measure.
- *
- * Context: User context only.  This function may sleep.
- *
- * Get the size of a NUL-terminated string in user space.
- *
- * Returns the size of the string INCLUDING the terminating NUL.
- * On exception, returns 0.
- *
- * If there is a limit on the length of a valid string, you may wish to
- * consider using strnlen_user() instead.
- */
-long strlen_user(const char __user *str)
-{
-	unsigned long max_addr, src_addr;
+		str = masked_user_read_access_begin(str);
+		retval = do_strnlen_user(str, count, count);
+		user_read_access_end();
+		return retval;
+	}
 
-	max_addr = user_addr_max();
-	src_addr = (unsigned long)str;
+	max_addr = TASK_SIZE_MAX;
+	src_addr = (unsigned long)untagged_addr(str);
 	if (likely(src_addr < max_addr)) {
 		unsigned long max = max_addr - src_addr;
-		return do_strnlen_user(str, ~0ul, max);
+		long retval;
+
+		/*
+		 * 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 (user_read_access_begin(str, max)) {
+			retval = do_strnlen_user(str, count, max);
+			user_read_access_end();
+			return retval;
+		}
 	}
 	return 0;
 }
-EXPORT_SYMBOL(strlen_user);
+EXPORT_SYMBOL(strnlen_user);