Messages in this thread | | | Date | Fri, 6 Oct 2023 16:58:18 -0700 | Subject | Re: [PATCH bpf v3] net/xdp: fix zero-size allocation warning in xskq_create() | From | Martin KaFai Lau <> |
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On 10/6/23 4:24 PM, Andrew Kanner wrote: >> Thanks for the explanation, so iiuc it means it will overflow the >> struct_size() first because of the is_power_of_2(nentries) requirement? >> Could you help adding some comment to explain? Thanks. >> > The overflow happens because there's no upper limit for nentries > (userspace input). Let me add more context, e.g. from net/xdp/xsk.c: > > static int xsk_setsockopt(struct socket *sock, int level, int optname, > sockptr_t optval, unsigned int optlen) > { > [...] > if (copy_from_sockptr(&entries, optval, sizeof(entries))) > return -EFAULT; > [...] > err = xsk_init_queue(entries, q, false); > [...] > } > > 'entries' is passed to xsk_init_queue() and there're 2 checks: for 0 > and is_power_of_2() only, no upper bound check: > > static int xsk_init_queue(u32 entries, struct xsk_queue **queue, > bool umem_queue) > { > struct xsk_queue *q; > > if (entries == 0 || *queue || !is_power_of_2(entries)) > return -EINVAL; > > q = xskq_create(entries, umem_queue); > if (!q) > return -ENOMEM; > [...] > } > > The 'entries' value is next passed to struct_size() in > net/xdp/xsk_queue.c. If it's large enough - SIZE_MAX will be returned.
All make sense. I was mostly asking to add a comment at the "if (unlikely(size == SIZE_MAX)" check to explain this details on why checking SIZE_MAX is enough.
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