On Fri, Sep 20, 2013 at 02:37:36PM +0300, Dan Carpenter wrote:
> The code here is trying to ensure that we don't have a
> "header_size + stack_size" which is more than USHRT_MAX. I changed
> the overflow check a little to make it more clear.
>
> My concern here is that if "header_size + sizeof(u64)" is very large
> then we could end up with underflow doing the subtraction and end up
> with a "stack_size" larger than intended.
>
> I don't know perf well enough to say if this is possible.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index dd236b6..eec9e683 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4217,11 +4217,13 @@ perf_sample_ustack_size(u16 stack_size, u16 header_size,
> header_size += 2 * sizeof(u64);
>
> /* Do we fit in with the current stack dump size? */
> - if ((u16) (header_size + stack_size) < header_size) {
> + if (header_size > USHRT_MAX - stack_size) {
hum, the original check looks clear enough to me
> /*
> * If we overflow the maximum size for the sample,
> * we customize the stack dump size to fit in.
> */
> + if (header_size + sizeof(u64) > USHRT_MAX)
> + return 0;
ok, I wonder if we could practically reach header size
this big, but it's safer to check
thanks,
jirka
> stack_size = USHRT_MAX - header_size - sizeof(u64);
> stack_size = round_up(stack_size, sizeof(u64));
> }
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