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Subject[PATCH v4 2/3] string.h: add memcpy_and_pad()
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This helper function is useful for the nvme subsystem, and maybe
others.

Note: the warnings reported by the kbuild test robot for this patch
are actually generated by the use of CONFIG_PROFILE_ALL_BRANCHES
together with __FORTIFY_INLINE.

Signed-off-by: Martin Wilck <mwilck@suse.com>
---
include/linux/string.h | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index a467e617eeb08..0bec4151b0eb9 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -200,6 +200,7 @@ static inline const char *kbasename(const char *path)
void fortify_panic(const char *name) __noreturn __cold;
void __read_overflow(void) __compiletime_error("detected read beyond size of object passed as 1st parameter");
void __read_overflow2(void) __compiletime_error("detected read beyond size of object passed as 2nd parameter");
+void __read_overflow3(void) __compiletime_error("detected read beyond size of object passed as 3rd parameter");
void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter");

#if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE)
@@ -395,4 +396,33 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q)

#endif

+/**
+ * memcpy_and_pad - Copy one buffer to another with padding
+ * @dest: Where to copy to
+ * @dest_len: The destination buffer size
+ * @src: Where to copy from
+ * @count: The number of bytes to copy
+ * @pad: Character to use for padding if space is left in destination.
+ */
+__FORTIFY_INLINE void memcpy_and_pad(void *dest, size_t dest_len,
+ const void *src, size_t count, int pad)
+{
+ size_t dest_size = __builtin_object_size(dest, 0);
+ size_t src_size = __builtin_object_size(src, 0);
+
+ if (__builtin_constant_p(dest_len) && __builtin_constant_p(count)) {
+ if (dest_size < dest_len && dest_size < count)
+ __write_overflow();
+ else if (src_size < dest_len && src_size < count)
+ __read_overflow3();
+ }
+ if (dest_size < dest_len)
+ fortify_panic(__func__);
+ if (dest_len > count) {
+ memcpy(dest, src, count);
+ memset(dest + count, pad, dest_len - count);
+ } else
+ memcpy(dest, src, dest_len);
+}
+
#endif /* _LINUX_STRING_H_ */
--
2.14.0
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