Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso...

[karo-tx-linux.git] / include / linux / random.h

diff --git a/include/linux/random.h b/include/linux/random.h
index 4aecc339558d5ea1a30e73b8e9889b0cee34f961..eafea6a09361f8787bad4aa22d906dc17177d03f 100644 (file)
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -58,6 +58,27 @@ static inline unsigned long get_random_long(void)
 #endif
 }
 
+/*
+ * On 64-bit architectures, protect against non-terminated C string overflows
+ * by zeroing out the first byte of the canary; this leaves 56 bits of entropy.
+ */
+#ifdef CONFIG_64BIT
+# ifdef __LITTLE_ENDIAN
+#  define CANARY_MASK 0xffffffffffffff00UL
+# else /* big endian, 64 bits: */
+#  define CANARY_MASK 0x00ffffffffffffffUL
+# endif
+#else /* 32 bits: */
+# define CANARY_MASK 0xffffffffUL
+#endif
+
+static inline unsigned long get_random_canary(void)
+{
+       unsigned long val = get_random_long();
+
+       return val & CANARY_MASK;
+}
+
 /* Calls wait_for_random_bytes() and then calls get_random_bytes(buf, nbytes).
  * Returns the result of the call to wait_for_random_bytes. */
 static inline int get_random_bytes_wait(void *buf, int nbytes)