Messages in this thread | | | Date | Tue, 24 Oct 2023 13:50:34 -0600 | From | "Gustavo A. R. Silva" <> | Subject | [RFC - is this a bug?] wifi: ath10k: Asking for some light on this, please :) |
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Hi all,
While working on tranforming one-element array `peer_chan_list` in `struct wmi_tdls_peer_capabilities` into a flex-array member
7187 struct wmi_tdls_peer_capabilities { ... 7199 struct wmi_channel peer_chan_list[1]; 7200 } __packed;
the following line caught my attention:
./drivers/net/wireless/ath/ath10k/wmi.c: 8920 memset(skb->data, 0, sizeof(*cmd));
Notice that before the flex-array transformation, we are zeroing 128 bytes in `skb->data` because `sizeof(*cmd) == 128`, see below:
$ pahole -C wmi_10_4_tdls_peer_update_cmd drivers/net/wireless/ath/ath10k/wmi.o struct wmi_10_4_tdls_peer_update_cmd { __le32 vdev_id; /* 0 4 */ struct wmi_mac_addr peer_macaddr; /* 4 8 */ __le32 peer_state; /* 12 4 */ __le32 reserved[4]; /* 16 16 */ struct wmi_tdls_peer_capabilities peer_capab; /* 32 96 */
/* size: 128, cachelines: 2, members: 5 */ };
So, after the flex-array transformation (and the necessary adjustments to a few other lines of code) we would be zeroing 104 bytes in `skb->data` because `sizeof(*cmd) == 104`, see below:
$ pahole -C wmi_10_4_tdls_peer_update_cmd drivers/net/wireless/ath/ath10k/wmi.o struct wmi_10_4_tdls_peer_update_cmd { __le32 vdev_id; /* 0 4 */ struct wmi_mac_addr peer_macaddr; /* 4 8 */ __le32 peer_state; /* 12 4 */ __le32 reserved[4]; /* 16 16 */ struct wmi_tdls_peer_capabilities peer_capab; /* 32 72 */
/* size: 104, cachelines: 2, members: 5 */ /* last cacheline: 40 bytes */ };
This difference arises because the size of the element type for the `peer_chan_list` array, which is `sizeof(struct wmi_channel) == 24 `
$ pahole -C wmi_channel drivers/net/wireless/ath/ath10k/wmi.o struct wmi_channel { __le32 mhz; /* 0 4 */ __le32 band_center_freq1; /* 4 4 */ __le32 band_center_freq2; /* 8 4 */
[..] /* 20 4 */
/* size: 24, cachelines: 1, members: 6 */ /* last cacheline: 24 bytes */ };
is included in `sizeof(*cmd)` before the transformation.
So, my question is: do we really need to zero out those extra 24 bytes in `skb->data`? or is it rather a bug in the original code?
Thanks! -- Gustavo
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