On Mon, 19 May 2025 09:02:40 +0200
Rafal Bilkowski <rafalbilkow...@gmail.com> wrote:
> Add a check in trace_iter_expand_format to prevent integer overflow when
> calculating the new format buffer size, and to handle the case where krealloc
> returns ZERO_SIZE_PTR. This improves robustness and prevents potential
> memory corruption or kernel crashes.
What exactly is this trying to protect?
>
> Signed-off-by: Rafal Bilkowski <rafalbilkow...@gmail.com>
> ---
> kernel/trace/trace.c | 4 ++++
> kernel/trace/trace_output.c | 2 ++
> 2 files changed, 6 insertions(+)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 5b8db27fb6ef..637bd1ff9325 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3596,6 +3596,10 @@ char *trace_iter_expand_format(struct trace_iterator
> *iter)
> if (!iter->tr || iter->fmt == static_fmt_buf)
> return NULL;
>
> + /* Protection against overflow and ZERO_SIZE_PTR returned from krealloc
> */
> + if (check_add_overflow(iter->fmt_size, STATIC_FMT_BUF_SIZE,
> &iter->fmt_size))
> + return NULL;
This will *NEVER* happen!
The fmt_size is initialized as STATIC_FMT_BUF_SIZE, and this is the only
function that increases it, and that happens *only* if the krealloc() succeeds.
For this to happen, then the krealloc must have allocated something that
would allow the format size to be INT_MAX, which krealloc would fail much
earlier than that.
Not to mention, the formats can't be more that the sub-buffer size, which
is by default 4K and can be at most 64K. Way smaller than INT_MAX.
> +
> tmp = krealloc(iter->fmt, iter->fmt_size + STATIC_FMT_BUF_SIZE,
> GFP_KERNEL);
> if (tmp) {
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index b9ab06c99543..42560027001a 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -979,6 +979,8 @@ static void print_fields(struct trace_iterator *iter,
> struct trace_event_call *c
> iter->fmt_size);
> if (ret < 0)
> trace_seq_printf(&iter->seq, "(0x%px)", pos);
> + else if (ret == 0)
> + trace_seq_printf(&iter->seq, "(0x%px:<NULL>)",
> pos);
This part I'm OK with adding.
-- Steve
> else
> trace_seq_printf(&iter->seq, "(0x%px:%s)",
> pos, iter->fmt);
