Re: [PATCH net 1/6] net: bcmasp: fix mib counters struct alignment with ethtool stats

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- [Medium] The commit message overstates what the bug did.

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net: bcmasp: fix mib counters struct alignment with ethtool stats

This commit removes the leftover edpkt_* fields from the start of struct
bcmasp_mib_counters. They were left in place when the matching
bcmasp_gstrings_stats[] entries were removed for asp-v3.0. Since then the
struct layout has not matched the order the ethtool code indexes by.

Because bcmasp_update_mib_counters() and bcmasp_get_ethtool_stats() index
into struct bcmasp_mib_counters sequentially based on the order of
bcmasp_gstrings_stats, this 16-byte offset caused hardware statistics
to be written to the wrong struct members and software counters to be
read from incorrect offsets (and reading out-of-bounds at the end of the
struct).

[Severity: Medium]
Is the out-of-bounds part of this description accurate?

Before this patch, struct bcmasp_mib_counters had 17 u32 members (68
bytes), and bcmasp_gstrings_stats[] has 13 entries. Both loops stop at
BCMASP_STATS_LEN:

drivers/net/ethernet/broadcom/asp2/bcmasp_ethtool.c:bcmasp_get_ethtool_stats() {
    ...
	for (i = 0; i < BCMASP_STATS_LEN; i++) {
		p = (char *)(&intf->mib) + (i * sizeof(u32));
		data[i] = *(u32 *)p;
	}
}

So the highest offset either loop touches is 12 * 4 = 48 bytes, which is
inside the 68-byte struct.

The hardware values also appear to have reached userspace correctly.
bcmasp_update_mib_counters() writes them to raw slots 0-4, and
bcmasp_get_ethtool_stats() reads them back from the same slots. The only
members overwritten were edpkt_* and umac_frm_cnt, and no code uses those
by name.

The part that looks broken is the software counters. Code increments them
by name (intf->mib.alloc_rx_skb_failed++, tx_dma_failed++, and so on).
They sit in raw slots 9-16, but ethtool read slots 5-12. As a result:

  - "RX SKB Alloc Failed", "TX DMA Failed", "Multicast Filters Full" and
    "Unicast Filters Full" read fb_* members that are never written, so
    they always showed 0.

  - The next four strings showed the values of the first four software
    counters.

  - filters_combine_cnt, promisc_filters_cnt, tx_realloc_offload_failed
    and tx_timeout_cnt were never shown at all.

Could the commit message describe this as shifted or mislabeled software
counters, rather than as an out-of-bounds read at the end of the struct?

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Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260922221630.3864427-1-florian.fainelli%40broadcom.com