On Thu, 2012-12-06 at 18:09 +0100, Sylvain Munaut wrote:
> The "%5lu" part of the sprintf only guarantees a minimum length,
> not a maximum one. This patch should make it correct for any
> possible timestamp.
>
> This problem dates back from the printk conversion to records AFAICT.
>
> I've tested this locally both by verifying 'dmesg' no longer
> segfaulted and also by checking that before this patch the
> buffer was overrun by exactly the number of char corresponding to
> extra digits in the timestamps.
>
> Cc: Kay Sievers <k...@vrfy.org>
> Cc: sta...@kernel.org
> Signed-off-by: Sylvain Munaut <s.mun...@whatever-company.com>
> ---
> kernel/printk.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/printk.c b/kernel/printk.c
> index 66a2ea3..2ceceea 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -847,8 +847,17 @@ static size_t print_time(u64 ts, char *buf)
> if (!printk_time)
> return 0;
>
> - if (!buf)
> - return 15;
> + if (!buf) {
> + size_t len = 15;
> + u64 ts_limit = (u64)100000 * (u64)1000000000;
> +
> + while ((ts > ts_limit) && (len < 21)) {
> + len++;
> + ts_limit = 10 * ts_limit;
> + }
Perhaps use snprintf for sizing something like below?
(untested/uncompiled)
static size_t print_time(u64 ts, char *buf)
{
unsigned long rem_nsec;
char *tmpbuf = buf;
int size = 15; /* expected size of non-null buf */
char local_buf[1];
if (!printk_time)
return 0;
if (!buf) { /* emit to a dummy buf instead */
tmpbuf = local_buf;
size = sizeof(local_buf);
}
rem_nsec = do_div(ts, 1000000000);
return snprintf(tmpbuf, size, "[%5lu.%06lu] ",
(unsigned long)ts, rem_nsec / 1000);
}
It's perhaps unfortunate that print_time doesn't take a
a buffer and a size_t of buffer.
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