From: Alexey Dobriyan 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 Signed-off-by: Andrew Morton --- include/linux/string.h | 1 + mm/util.c | 18 ++++++++++++++++++ 2 files changed, 19 insertions(+) diff -puN include/linux/string.h~kmemdup-introduce include/linux/string.h --- a/include/linux/string.h~kmemdup-introduce +++ a/include/linux/string.h @@ -99,6 +99,7 @@ extern void * memchr(const void *,int,__ #endif extern char *kstrdup(const char *s, gfp_t gfp); +extern void *kmemdup(const void *src, size_t len, gfp_t gfp); #ifdef __cplusplus } diff -puN mm/util.c~kmemdup-introduce mm/util.c --- a/mm/util.c~kmemdup-introduce +++ a/mm/util.c @@ -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 * _