On Sat, Apr 19, 2014 at 10:15:07AM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <eduma...@google.com>
>
> A va_list needs to be copied in case it needs to be used twice.
>
> Thanks to Hugh for debugging this issue, leading to various panics.
>
> Tested:
>
> lpq84:~# echo "|/foobar12345 %h %h %h %h %h %h %h %h %h %h %h %h %h %h %
> h %h %h %h %h %h" >/proc/sys/kernel/core_pattern
>
> 'produce_core' is simply : main() { *(int *)0 = 1;}
>
> lpq84:~# ./produce_core
> Segmentation fault (core dumped)
> lpq84:~# dmesg | tail -1
> [ 614.352947] Core dump to |/foobar12345 lpq84 lpq84 lpq84 lpq84 lpq84
> lpq84 lpq84 lpq84 lpq84 lpq84 lpq84 lpq84 lpq84 lpq84 lpq84 lpq84 lpq84
> lpq84 lpq84 (null) pipe failed
>
> Notice the last argument was replaced by a NULL (we were lucky enough to
> not crash, but do not try this on your production machine !)
>
> After fix :
>
> lpq83:~# echo "|/foobar12345 %h %h %h %h %h %h %h %h %h %h %h %h %h %h %
> h %h %h %h %h %h" >/proc/sys/kernel/core_pattern
> lpq83:~# ./produce_core
> Segmentation fault
> lpq83:~# dmesg | tail -1
> [ 740.800441] Core dump to |/foobar12345 lpq83 lpq83 lpq83 lpq83 lpq83
> lpq83 lpq83 lpq83 lpq83 lpq83 lpq83 lpq83 lpq83 lpq83 lpq83 lpq83 lpq83
> lpq83 lpq83 lpq83 pipe failed
>
> Fixes: 5fe9d8ca21cc ("coredump: cn_vprintf() has no reason to call
> vsnprintf() twice")
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Diagnosed-by: Hugh Dickins <hu...@google.com>
> Cc: Oleg Nesterov <o...@redhat.com>
> Cc: Neil Horman <nhor...@tuxdriver.com>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: sta...@vger.kernel.org # 3.11+
> ---
>
> Note: This patch applies cleanly to 3.11+ but might need some
> adjustments for older linux kernels...
>
> fs/coredump.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index e3ad709a4232..0b2528fb640e 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -73,10 +73,15 @@ static int expand_corename(struct core_name *cn, int size)
> static int cn_vprintf(struct core_name *cn, const char *fmt, va_list arg)
> {
> int free, need;
> + va_list arg_copy;
>
> again:
> free = cn->size - cn->used;
> - need = vsnprintf(cn->corename + cn->used, free, fmt, arg);
> +
> + va_copy(arg_copy, arg);
> + need = vsnprintf(cn->corename + cn->used, free, fmt, arg_copy);
> + va_end(arg_copy);
> +
> if (need < free) {
> cn->used += need;
> return 0;
>
>
>
Thanks Eric!
Acked-by: Neil Horman <nhor...@tuxdriver.com>
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