linux-kernel - Re: [PATCH v4] core_pattern: fix long parameters was truncated by core

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Date:	Tue, 24 Aug 2010 15:47:45 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Xiaotian Feng <dfeng@...hat.com>
Cc:	linux-fsdevel@...r.kernel.org, nhorman@...driver.com,
	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [PATCH v4] core_pattern: fix long parameters was truncated by
 core_pattern handler

On Tue, 24 Aug 2010 17:42:46 +0800
Xiaotian Feng <dfeng@...hat.com> 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)?

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