Commit 1a2f67b4 authored Sep 30, 2006 by Alexey Dobriyan Committed by Linus Torvalds Oct 01, 2006

[PATCH] kmemdup: introduce



One of idiomatic ways to duplicate a region of memory is

	dst = kmalloc(len, GFP_KERNEL);
	if (!dst)
		return -ENOMEM;
	memcpy(dst, src, len);

which is neat code except a programmer needs to write size twice.  Which
sometimes leads to mistakes.  If len passed to kmalloc is smaller that len
passed to memcpy, it's straight overwrite-beyond-end.  If len passed to
memcpy is smaller than len passed to kmalloc, it's either a) legit
behaviour ;-), or b) cloned buffer will contain garbage in second half.

Slight trolling of commit lists shows several duplications bugs
done exactly because of diverged lenghts:

	Linux:
		[CRYPTO]: Fix memcpy/memset args.
		[PATCH] memcpy/memset fixes
	OpenBSD:
		kerberosV/src/lib/asn1: der_copy.c:1.4

If programmer is given only one place to play with lengths, I believe, such
mistakes could be avoided.

With kmemdup, the snippet above will be rewritten as:

	dst = kmemdup(src, len, GFP_KERNEL);
	if (!dst)
		return -ENOMEM;

This also leads to smaller code (kzalloc effect). Quick grep shows
200+ places where kmemdup() can be used.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 9442e691

include/linux/string.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -99,6 +99,7 @@ extern void * memchr(const void *,int,__kernel_size_t);
		#endif

		extern char kstrdup(const char s, gfp_t gfp);
		extern void kmemdup(const void src, size_t len, gfp_t gfp);

		#ifdef __cplusplus
		}

mm/util.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -40,6 +40,24 @@ char kstrdup(const char s, gfp_t gfp)
		}
		EXPORT_SYMBOL(kstrdup);

		/**
		* kmemdup - duplicate region of memory
		*
		* @src: memory region to duplicate
		* @len: memory region length
		* @gfp: GFP mask to use
		*/
		void kmemdup(const void src, size_t len, gfp_t gfp)
		{
		void *p;

		p = ____kmalloc(len, gfp);
		if (p)
		memcpy(p, src, len);
		return p;
		}
		EXPORT_SYMBOL(kmemdup);

		/*
		* strndup_user - duplicate an existing string from user space
		*

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