Re: [PATCH] lib: introduce strdup_from_user

[Alexey Dobriyan]

NAK
It accesses userspace data twice.

On Fri, Jun 3, 2011 at 7:45 PM, Timur Tabi <timur@xxxxxxxxxxxxx> wrote:
> Add function strdup_from_user(), which kmallocs a block of memory and
> copies a user-space NULL-terminated string into it.  NULL is returned if
> the string is too large or cannot be accessed.
>
> This function is added to lib/string_helpers.c, so this file is repurposed
> to store generic "string helper" functions, and not just a function to
> assist in sprintfs.
>
> Signed-off-by: Timur Tabi <timur@xxxxxxxxxxxxx>
> ---
>  include/linux/string_helpers.h |    2 +
>  lib/string_helpers.c           |   43 +++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 44 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
> index a3eb2f6..6231838 100644
> --- a/include/linux/string_helpers.h
> +++ b/include/linux/string_helpers.h
> @@ -13,4 +13,6 @@ enum string_size_units {
>  int string_get_size(u64 size, enum string_size_units units,
>                    char *buf, int len);
>
> +char *strdup_from_user(const char __user *ustr, size_t max);
> +
>  #endif
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index ab431d4..61323e6 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -1,13 +1,19 @@
>  /*
> - * Helpers for formatting and printing strings
> + * Additional arch-independent string helper functions
>  *
>  * Copyright 31 August 2008 James Bottomley
> + * Copyright (C) 2011 Freescale Semiconductor, Inc.
> + *
>  */
>  #include <linux/kernel.h>
>  #include <linux/math64.h>
>  #include <linux/module.h>
>  #include <linux/string_helpers.h>
>
> +#include <linux/slab.h>
> +#include <linux/err.h>
> +#include <asm/uaccess.h>
> +
>  /**
>  * string_get_size - get the size in the specified units
>  * @size:      The size to be converted
> @@ -66,3 +72,38 @@ int string_get_size(u64 size, const enum string_size_units units,
>        return 0;
>  }
>  EXPORT_SYMBOL(string_get_size);
> +
> +/**
> + * strdup_from_user - copy a user-space string to a kmalloc'd buffer
> + * @ustr: user-space pointer to null-terminated string
> + * @max: maximum size the string is allowed to be, include NULL terminator
> + *
> + * This function allocates a block of memory (using kmalloc) and copies a
> + * user-space string into that buffer.  It returns a pointer to that string,
> + * or an error code.
> + */
> +char *strdup_from_user(const char __user *ustr, size_t max)
> +{
> +       size_t len;
> +       char *str;
> +
> +       len = strnlen_user(ustr, max);
> +       if (len >= max)
> +               return ERR_PTR(-ENAMETOOLONG);
> +
> +       /* strnlen_user returns 0 on access error */
> +       if (!len)
> +               return ERR_PTR(-EFAULT);
> +
> +       str = kzalloc(len, GFP_KERNEL);
> +       if (!str)
> +               return ERR_PTR(-ENOMEM);
> +
> +       if (copy_from_user(str, ustr, len)) {
> +               kfree(str);
> +               return ERR_PTR(-EFAULT);
> +       }
> +
> +       return str;
> +}
> +EXPORT_SYMBOL(strdup_from_user);
> --
> 1.7.3.4
>
>
> --
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