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

Andrew Morton
2010-08-24T22:48:17Z

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