linux-kernel - Re: [RFC][PATCH] kmemdup_from

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Message-ID: <20090306072328.GL22605@hack.private>
Date:	Fri, 6 Mar 2009 15:23:28 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] kmemdup_from_user(): introduce

On Fri, Mar 06, 2009 at 03:04:12PM +0800, Li Zefan wrote:
>I notice there are many places doing copy_from_user() which follows
>kmalloc():
>
>        dst = kmalloc(len, GFP_KERNEL);
>        if (!dst)
>                return -ENOMEM;
>        if (copy_from_user(dst, src, len)) {
>		kfree(dst);
>		return -EFAULT
>	}
>
>kmemdup_from_user() is a wrapper of the above code. With this new
>function, we don't have to write 'len' twice, which can lead to
>typos/mistakes. It also produces smaller code.
>
>A qucik grep shows 250+ places where kmemdup_from_user() *may* be
>used. I'll prepare a patchset to do this conversion.
>
>Signed-off-by: Li Zefan <lizf@...fujitsu.com>
>---
> include/linux/string.h |    1 +
> mm/util.c              |   24 ++++++++++++++++++++++++
> 2 files changed, 25 insertions(+), 0 deletions(-)
>
>diff --git a/include/linux/string.h b/include/linux/string.h
>index 76ec218..397e622 100644
>--- a/include/linux/string.h
>+++ b/include/linux/string.h
>@@ -105,6 +105,7 @@ extern void * memchr(const void *,int,__kernel_size_t);
> extern char *kstrdup(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 void *kmemdup_from_user(const void __user *src, 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 37eaccd..a608ebb 100644
>--- a/mm/util.c
>+++ b/mm/util.c
>@@ -70,6 +70,30 @@ void *kmemdup(const void *src, size_t len, gfp_t gfp)
> EXPORT_SYMBOL(kmemdup);
> 
> /**
>+ * kmemdup_from_user - duplicate memory region from user space
>+ *
>+ * @src: source address in user space
>+ * @len: number of bytes to copy
>+ * @gfp: GFP mask to use
>+ */
>+void *kmemdup_from_user(const void __user *src, size_t len, gfp_t gfp)
>+{
>+	void *p;
>+
>+	p = kmalloc_track_caller(len, gfp);


Well, you use kmalloc_track_caller, instead of kmalloc as you showed
above. :) Why don't you mention this?


>+	if (!p)
>+		return ERR_PTR(-ENOMEM);
>+
>+	if (copy_from_user(p, src, len)) {
>+		kfree(p);
>+		return ERR_PTR(-EFAULT);
>+	}
>+
>+	return p;
>+}
>+EXPORT_SYMBOL(kmemdup_from_user);
>+
>+/**
>  * __krealloc - like krealloc() but don't free @p.
>  * @p: object to reallocate memory for.
>  * @new_size: how many bytes of memory are required.
>-- 
>1.5.4.rc3
>--
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-- 
Do what you love, f**k the rest! F**k the regulations!
 
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