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SubjectRe: [PATCH] relay: Fix type mismatch when allocating memory in relay_create_buf()
On Tue, 29 Nov 2022 09:23:38 +0000 Gavrilov Ilia <Ilia.Gavrilov@infotecs.ru> wrote:

> The 'padding' field of the 'rchan_buf' structure is an array of 'size_t'
> elements, but the memory is allocated for an array of 'size_t *' elements.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -148,13 +148,13 @@ static struct rchan_buf *relay_create_buf(struct rchan *chan)
> {
> struct rchan_buf *buf;
>
> - if (chan->n_subbufs > KMALLOC_MAX_SIZE / sizeof(size_t *))
> + if (chan->n_subbufs > KMALLOC_MAX_SIZE / sizeof(size_t))
> return NULL;
>
> buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
> if (!buf)
> return NULL;
> - buf->padding = kmalloc_array(chan->n_subbufs, sizeof(size_t *),
> + buf->padding = kmalloc_array(chan->n_subbufs, sizeof(size_t),
> GFP_KERNEL);

This is why I prefer kmalloc_array(N, sizeof(*(buf->padding)), ...)

Because the reviewer doesn't have to go check that the types match up,
and because the code doesn't need changing if the type of
*(buf->padding) is changed.

Others don't like this practice, but I forget why.

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