Subject: Re: [net-next PATCH v4 1/3] sysctl: refactor integer handling proc code

From: Cong Wang <[email-masked]>
Date: Tue, 16 Feb 2010 16:41:07 +0800

Octavian Purdila wrote:
> As we are about to add another integer handling proc function a little
> bit of cleanup is in order: add a few helper functions to improve code
> readability and decrease code duplication.
> 
> In the process a bug is fixed as well: if the user specifies a number
> with more then 20 digits it will be interpreted as two integers
> (e.g. 10000...13 will be interpreted as 100.... and 13).
> 
> Signed-off-by: Octavian Purdila <[email-masked]>
> Cc: WANG Cong <[email-masked]>
> Cc: Eric W. Biederman <[email-masked]>

Some comments below.

> ---
>  kernel/sysctl.c |  298 +++++++++++++++++++++++++++----------------------------
>  1 files changed, 144 insertions(+), 154 deletions(-)
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 8a68b24..b0f9618 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2039,8 +2039,98 @@ int proc_dostring(struct ctl_table *table, int write,
>  			       buffer, lenp, ppos);
>  }
>  
> +static int proc_skip_wspace(char __user **buf, size_t *size)
> +{
> +	char c;
> +
> +	while (*size) {
> +		if (get_user(c, *buf))
> +			return -EFAULT;
> +		if (!isspace(c))
> +			break;
> +		(*size)--; (*buf)++;
> +	}
> +
> +	return 0;
> +}

In lib/string.c we have skip_spaces(), I think we can use it
here instead of inventing another one.

> +
> +#define TMPBUFLEN 22
> +static int proc_get_next_ulong(char __user **buf, size_t *size,
> +			       unsigned long *val, bool *neg)
> +{
> +	int len;
> +	char *p, tmp[TMPBUFLEN];
> +	int err;
> +
> +	err = proc_skip_wspace(buf, size);
> +	if (err)
> +		return err;
> +	if (!*size)
> +		return -EINVAL;
> +
> +	len = *size;
> +	if (len > TMPBUFLEN-1)
> +		len = TMPBUFLEN-1;
> +
> +	if (copy_from_user(tmp, *buf, len))
> +		return -EFAULT;
> +
> +	tmp[len] = 0;
> +	p = tmp;
> +	if (*p == '-' && *size > 1) {
> +		*neg = 1;
> +		p++;
> +	} else
> +		*neg = 0;
> +	if (*p < '0' || *p > '9')
> +		return -EINVAL;

isdigit().

> +
> +	*val = simple_strtoul(p, &p, 0);
> +
> +	len = p - tmp;
> +	if (((len < *size) && *p && !isspace(*p)) ||
> +	    /* We don't know if the next char is whitespace thus we may accept
> +	     * invalid integers (e.g. 1234...a) or two integers instead of one
> +	     * (e.g. 123...1). So lets not allow such large numbers. */
> +	    len == TMPBUFLEN - 1)
> +		return -EINVAL;
>  
> -static int do_proc_dointvec_conv(int *negp, unsigned long *lvalp,
> +	*buf += len; *size -= len;
> +
> +	return 0;
> +}
> +
> +static int proc_put_ulong(char __user **buf, size_t *size, unsigned long val,
> +			  bool neg, bool first)
> +{
> +	int len;
> +	char tmp[TMPBUFLEN], *p = tmp;
> +
> +	if (!first)
> +		*p++ = '\t';
> +	sprintf(p, "%s%lu", neg ? "-" : "", val);
> +	len = strlen(tmp);
> +	if (len > *size)
> +		len = *size;
> +	if (copy_to_user(*buf, tmp, len))
> +		return -EFAULT;
> +	*size -= len;
> +	*buf += len;
> +	return 0;
> +}
> +#undef TMPBUFLEN
> +
> +static int proc_put_newline(char __user **buf, size_t *size)
> +{
> +	if (*size) {
> +		if (put_user('\n', *buf))
> +			return -EFAULT;
> +		(*size)--, (*buf)++;
> +	}
> +	return 0;
> +}
> +
> +static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
>  				 int *valp,
>  				 int write, void *data)
>  {
> @@ -2049,7 +2139,7 @@ static int do_proc_dointvec_conv(int *negp, unsigned long *lvalp,
>  	} else {
>  		int val = *valp;
>  		if (val < 0) {
> -			*negp = -1;
> +			*negp = 1;
>  			*lvalp = (unsigned long)-val;
>  		} else {
>  			*negp = 0;
> @@ -2060,19 +2150,15 @@ static int do_proc_dointvec_conv(int *negp, unsigned long *lvalp,
>  }
>  
>  static int __do_proc_dointvec(void *tbl_data, struct ctl_table *table,
> -		  int write, void __user *buffer,
> +		  int write, void __user *_buffer,
>  		  size_t *lenp, loff_t *ppos,
> -		  int (*conv)(int *negp, unsigned long *lvalp, int *valp,
> +		  int (*conv)(bool *negp, unsigned long *lvalp, int *valp,
>  			      int write, void *data),
>  		  void *data)
>  {
> -#define TMPBUFLEN 21
> -	int *i, vleft, first = 1, neg;
> -	unsigned long lval;
> -	size_t left, len;
> -	
> -	char buf[TMPBUFLEN], *p;
> -	char __user *s = buffer;
> +	int *i, vleft, first = 1, err = 0;
> +	size_t left;
> +	char __user *buffer = (char __user *) _buffer;
>  	
>  	if (!tbl_data || !table->maxlen || !*lenp ||
>  	    (*ppos && !write)) {
> @@ -2088,88 +2174,39 @@ static int __do_proc_dointvec(void *tbl_data, struct ctl_table *table,
>  		conv = do_proc_dointvec_conv;
>  
>  	for (; left && vleft--; i++, first=0) {
> -		if (write) {
> -			while (left) {
> -				char c;
> -				if (get_user(c, s))
> -					return -EFAULT;
> -				if (!isspace(c))
> -					break;
> -				left--;
> -				s++;
> -			}
> -			if (!left)
> -				break;
> -			neg = 0;
> -			len = left;
> -			if (len > sizeof(buf) - 1)
> -				len = sizeof(buf) - 1;
> -			if (copy_from_user(buf, s, len))
> -				return -EFAULT;
> -			buf[len] = 0;
> -			p = buf;
> -			if (*p == '-' && left > 1) {
> -				neg = 1;
> -				p++;
> -			}
> -			if (*p < '0' || *p > '9')
> -				break;
> -
> -			lval = simple_strtoul(p, &p, 0);
> +		unsigned long lval;
> +		bool neg;
>  
> -			len = p-buf;
> -			if ((len < left) && *p && !isspace(*p))
> +		if (write) {
> +			err = proc_get_next_ulong(&buffer, &left, &lval, &neg);
> +			if (err)
>  				break;
> -			s += len;
> -			left -= len;
> -
>  			if (conv(&neg, &lval, i, 1, data))
>  				break;
>  		} else {
> -			p = buf;
> -			if (!first)
> -				*p++ = '\t';
> -	
>  			if (conv(&neg, &lval, i, 0, data))
>  				break;
> -
> -			sprintf(p, "%s%lu", neg ? "-" : "", lval);
> -			len = strlen(buf);
> -			if (len > left)
> -				len = left;
> -			if(copy_to_user(s, buf, len))
> -				return -EFAULT;
> -			left -= len;
> -			s += len;
> -		}
> -	}
> -
> -	if (!write && !first && left) {
> -		if(put_user('\n', s))
> -			return -EFAULT;
> -		left--, s++;
> -	}
> -	if (write) {
> -		while (left) {
> -			char c;
> -			if (get_user(c, s++))
> -				return -EFAULT;
> -			if (!isspace(c))
> +			err = proc_put_ulong(&buffer, &left, lval, neg, first);
> +			if (err)
>  				break;
> -			left--;
>  		}
>  	}
> -	if (write && first)
> -		return -EINVAL;
> +
> +	if (!write && !first && left && !err)
> +		err = proc_put_newline(&buffer, &left);
> +	if (write && !err)
> +		err = proc_skip_wspace(&buffer, &left);
> +	if (err == -EFAULT /* do we really need to check for -EFAULT? */ ||
> +	    (write && first))
> +		return err ? : -EINVAL;

The logic here seems messy, adding one or two goto's may help?

>  	*lenp -= left;
>  	*ppos += *lenp;
>  	return 0;
> -#undef TMPBUFLEN
>  }

The rest looks fine.

Thanks!