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Subject[RFC PATCH 1/4] mm/util: add kstrdup_const
Date
The patch adds alternative version of kstrdup which returns pointer
to constant char array. The function checks if input string is in
persistent and read-only memory section, if yes it returns the input string,
otherwise it fallbacks to kstrdup.
kstrdup_const is accompanied by kfree_const performing conditional memory
deallocation of the string.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
---
include/linux/string.h | 3 +++
mm/util.c | 22 ++++++++++++++++++++++
2 files changed, 25 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index a0c6fd5..c9cd44e 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -115,7 +115,10 @@ extern void * memchr(const void *,int,__kernel_size_t);
#endif
void *memchr_inv(const void *s, int c, size_t n);

+extern void kfree_const(const void *x);
+
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 char *kstrimdup(const char *s, gfp_t gfp);
extern void *kmemdup(const void *src, size_t len, gfp_t gfp);
diff --git a/mm/util.c b/mm/util.c
index d25558b..7fc0094 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -13,10 +13,24 @@
#include <linux/hugetlb.h>
#include <linux/vmalloc.h>

+#include <asm/sections.h>
#include <asm/uaccess.h>

#include "internal.h"

+static inline int is_kernel_rodata(unsigned long addr)
+{
+ return addr >= (unsigned long)__start_rodata &&
+ addr < (unsigned long)__end_rodata;
+}
+
+void kfree_const(const void *x)
+{
+ if (!is_kernel_rodata((unsigned long)x))
+ kfree(x);
+}
+EXPORT_SYMBOL(kfree_const);
+
/**
* kstrdup - allocate space for and copy an existing string
* @s: the string to duplicate
@@ -38,6 +52,14 @@ char *kstrdup(const char *s, gfp_t gfp)
}
EXPORT_SYMBOL(kstrdup);

+const char *kstrdup_const(const char *s, gfp_t gfp)
+{
+ if (is_kernel_rodata((unsigned long)s))
+ return s;
+
+ return kstrdup(s, gfp);
+}
+
/**
* kstrndup - allocate space for and copy an existing string
* @s: the string to duplicate
--
1.9.1


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