Re: [PATCH v4] core_pattern: fix long parameters was truncated bycore_pattern handler

[Xiaotian Feng]

On 08/25/2010 06:47 AM, Andrew Morton wrote:
> On Tue, 24 Aug 2010 17:42:46 +0800
> Xiaotian Feng<dfeng@xxxxxxxxxx>  wrote:
>
> > We met a parameter truncated issue, consider following:
> > > > echo "|/root/core_pattern_pipe_test %p /usr/libexec/blah-blah-blah \
> > %s %c %p %u %g 11 12345678901234567890123456789012345678 %t">  \
> > /proc/sys/kernel/core_pattern
> >
> > This is okay because the strings is less than CORENAME_MAX_SIZE.
> > "cat /proc/sys/kernel/core_pattern" shows the whole string. but
> > after we run core_pattern_pipe_test in man page, we found last
> > parameter was truncated like below:
> >          argc[10]=<12807486>
> >
> > The root cause is core_pattern allows % specifiers, which need to be
> > replaced during parse time, but the replace may expand the strings
> > to larger than CORENAME_MAX_SIZE. So if the last parameter is %
> > specifiers, the replace code is using snprintf(out_ptr, out_end - out_ptr, ...),
> > this will write out of corename array.
> >
> > Changes since v3:
> > make handling of single char also uses cn_printf, suggested by Andrew Morton.
> >
> > Changes since v2:
> > Introduced generic function cn_printf and make format_corename remember the time
> > has been expanded, suggested by Olg Nesterov and Neil Horman.
> >
> > Changes since v1:
> > This patch allocates corename at runtime, if the replace doesn't have enough
> > memory, expand the corename dynamically, suggested by Neil Horman.
> >
> > I've tested with some core_pattern strings, it works fine now.
>
> cool, thanks.
>
> > ...
> >
> > -static int format_corename(char *corename, long signr)
> > +static int format_corename(struct core_name *cn, long signr)
> >   {
> >   	const struct cred *cred = current_cred();
> >   	const char *pat_ptr = core_pattern;
> >   	int ispipe = (*pat_ptr == '|');
> > -	char *out_ptr = corename;
> > -	char *const out_end = corename + CORENAME_MAX_SIZE;
> > -	int rc;
> >   	int pid_in_pattern = 0;
> > +	int err = 0;
> > +
> > +	cn->size = CORENAME_MAX_SIZE * atomic_read(&call_count);
> > +	cn->corename = kmalloc(cn->size, GFP_KERNEL);
> > +	cn->used = 0;
> > +
> > +	if (!cn->corename)
> > +		return -ENOMEM;
> >
> >   	/* Repeat as long as we have more pattern to process and more output
> >   	   space */
> >   	while (*pat_ptr) {
> >   		if (*pat_ptr != '%') {
> > -			if (out_ptr == out_end)
> > -				goto out;
> > -			*out_ptr++ = *pat_ptr++;
> > +			err = cn_printf(cn, "%c", *pat_ptr++);
> >   		} else {
> >   			switch (*++pat_ptr) {
> > +			/* single % at the end, drop that */
> >   			case 0:
> > +				err = cn_printf(cn, "%c", '\0');
>
> Confused.  Doesn't this bit just add another \0 to the end of an
> already-null-terminated string?  And then make cn->used get out of sync
> with strlen(cn->corename)?
Good catch, I just realized the return value of vsnprintf is not 
including the trailing '\0', will follow an updated v5 patch. Thanks Andrew.


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