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Message-ID: <626ae2e7-66f8-423b-b17f-e75c1a6d29b3@embeddedor.com> Date: Tue, 24 Oct 2023 13:50:34 -0600 From: "Gustavo A. R. Silva" <gustavo@...eddedor.com> To: Kalle Valo <kvalo@...nel.org>, Jeff Johnson <quic_jjohnson@...cinc.com> Cc: ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org, "Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-hardening@...r.kernel.org Subject: [RFC - is this a bug?] wifi: ath10k: Asking for some light on this, please :) 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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