linux-kernel - Re: [Patch 1/3] sysctl: refactor integer handling proc code

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Message-Id: <201004091640.44056.opurdila@ixiacom.com>
Date:	Fri, 9 Apr 2010 16:40:43 +0300
From:	Octavian Purdila <opurdila@...acom.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Amerigo Wang <amwang@...hat.com>, linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	Neil Horman <nhorman@...driver.com>,
	David Miller <davem@...emloft.net>, ebiederm@...ssion.com
Subject: Re: [Patch 1/3] sysctl: refactor integer handling proc code


Hi and thanks for reviewing.

On Friday 09 April 2010 13:49:12 you wrote:
> > + *
> > + * In case of success 0 is returned and buf and size are updated with
> > + * the amount of bytes read. If tr is non NULL and a trailing
> > + * character exist (size is non zero after returning from this
> > + * function) tr is updated with the trailing character.
> > + */
> > +static int proc_get_ulong(char __user **buf, size_t *size,
> > +                         unsigned long *val, bool *neg,
> > +                         const char *perm_tr, unsigned perm_tr_len, char
> > *tr) +{
> > +       int len;
> > +       char *p, tmp[TMPBUFLEN];
> > +
> > +       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;
> 
> the function name implies that it is used to parse unsigned long, so
> negative value should not be supported.
> 

My intention was to signal that the argument is unsigned long and that the 
sign come separate in neg, but I am OK with changing the function name to 
proc_get_long() if you think that is better.

> > +       if (!isdigit(*p))
> > +               return -EINVAL;
> 
> It seems that ledding white space should be allowed, so this check
> isn't needed, and simple_strtoul can handle it.
> 

Leading white space is skipped with proc_skip_space before calling this 
function. AFAICS simple_strtoul does not handle whitespaces.

> > +
> > +       *val = simple_strtoul(p, &p, 0);
> > +
> > +       len = p - tmp;
> > +
> > +       /* 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. */ +       if (len == TMPBUFLEN - 1)
> > +               return -EINVAL;
> > +
> > +       if (len < *size && perm_tr_len && !isanyof(*p, perm_tr,
> > perm_tr_len)) +               return -EINVAL;
> 
> is strspn() better?
> 

I don't  think it will work out, \0 is an accepted trailer for many of the 
function which use this function.


> > +
> > +       if (tr && (len < *size))
> > +               *tr = *p;
> > +
> > +       *buf += len;
> > +       *size -= len;
> > +
> > +       return 0;
> > +}
> > +
> > +/**
> > + * proc_put_ulong - coverts an integer to a decimal ASCII formated
> > string + *
> > + * @buf - the user buffer
> > + * @size - the size of the user buffer
> > + * @val - the integer to be converted
> > + * @neg - sign of the number, %TRUE for negative
> > + * @first - if %FALSE will insert a separator character before the
> > number + * @separator - the separator character
> > + *
> > + * In case of success 0 is returned and buf and size are updated with
> > + * the amount of bytes read.
> > + */
> > +static int proc_put_ulong(char __user **buf, size_t *size, unsigned long
> > val, +                         bool neg, bool first, char separator)
> > +{
> > +       int len;
> > +       char tmp[TMPBUFLEN], *p = tmp;
> > +
> > +       if (!first)
> > +               *p++ = separator;
> > +       sprintf(p, "%s%lu", neg ? "-" : "", val);
> 
> negative should not be supported too.
> 

We need negatives in proc_dointvec, again we can change the function name if 
it will clear things up.

<snip>
> >                int val = *valp;
> >                unsigned long lval;
> >                if (val < 0) {
> > -                       *negp = -1;
> > +                       *negp = 1;
> >                        lval = (unsigned long)-val;
> >                } else {
> >                        *negp = 0;
> 
> These functions have so much lines of code. I think you can make them
> less. Please refer to strsep().
> 

Hmm, the input its pretty permissive and maybe this is why it looks so fat, we 
need to account for quite a few cases. 

Or maybe I spent too much time on this code already and I can't see the simple 
solution :)

Thanks,
tavi




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