Provide a function to create a NUL-terminated string from unterminated data

commit f35157417215ec138c920320c746fdb3e04ef1d5 upstream.

Provide a function, kmemdup_nul(), that will create a NUL-terminated string
from an unterminated character array where the length is known in advance.

This is better than kstrndup() in situations where we already know the
string length as the strnlen() in kstrndup() is superfluous.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/string.h b/include/linux/string.h
index aa30789b0f65eea407dfc56c68f9817c756f281d..98bb781a2effbbc08f9eb5c5f10fe22d1bf4bea9 100644 (file)
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -122,6 +122,7 @@ extern char *kstrdup(const char *s, gfp_t gfp);
 extern const char *kstrdup_const(const char *s, gfp_t gfp);
 extern char *kstrndup(const char *s, size_t len, gfp_t gfp);
 extern void *kmemdup(const void *src, size_t len, gfp_t gfp);
+extern char *kmemdup_nul(const char *s, size_t len, gfp_t gfp);
 
 extern char **argv_split(gfp_t gfp, const char *str, int *argcp);
 extern void argv_free(char **argv);

diff --git a/mm/util.c b/mm/util.c
index d5259b62f8d770eca8a9b1921fdd603f5f8be998..818bbae84721f4d877ac1054553b04bcb2419a91 100644 (file)
--- a/mm/util.c
+++ b/mm/util.c
@@ -80,6 +80,8 @@ EXPORT_SYMBOL(kstrdup_const);
  * @s: the string to duplicate
  * @max: read at most @max chars from @s
  * @gfp: the GFP mask used in the kmalloc() call when allocating memory
+ *
+ * Note: Use kmemdup_nul() instead if the size is known exactly.
  */
 char *kstrndup(const char *s, size_t max, gfp_t gfp)
 {
@@ -117,6 +119,28 @@ void *kmemdup(const void *src, size_t len, gfp_t gfp)
 }
 EXPORT_SYMBOL(kmemdup);
 
+/**
+ * kmemdup_nul - Create a NUL-terminated string from unterminated data
+ * @s: The data to stringify
+ * @len: The size of the data
+ * @gfp: the GFP mask used in the kmalloc() call when allocating memory
+ */
+char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
+{
+       char *buf;
+
+       if (!s)
+               return NULL;
+
+       buf = kmalloc_track_caller(len + 1, gfp);
+       if (buf) {
+               memcpy(buf, s, len);
+               buf[len] = '\0';
+       }
+       return buf;
+}
+EXPORT_SYMBOL(kmemdup_nul);
+
 /**
  * memdup_user - duplicate memory region from user space
  *