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Message-ID: <e19b9dcc-99d0-414d-95ef-69149daedaa9@embeddedor.com> Date: Tue, 24 Oct 2023 19:06:58 -0600 From: "Gustavo A. R. Silva" <gustavo@...eddedor.com> To: Kalle Valo <kvalo@...nel.org>, Jeff Johnson <quic_jjohnson@...cinc.com>, Manikanta Pubbisetty <quic_mpubbise@...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: Re: [RFC - is this a bug?] wifi: ath10k: Asking for some light on this, please :) [+CC Manikanta Pubbisetty ] As Johannes[1] pointed out, this `memset()` is probably unnecessary: ./drivers/net/wireless/ath/ath10k/wmi.c: 8920 memset(skb->data, 0, sizeof(*cmd)); However, the same exact issue[2] is present at the line below inside function `ath10k_wmi_alloc_skb()`: drivers/net/wireless/ath/ath10k/wmi.c: 1799 memset(skb->data, 0, round_len); Thanks -- Gustavo [1] https://lore.kernel.org/linux-hardening/26b15f4702cef17fe70b496a62f03735874bd16a.camel@sipsolutions.net/ [2] https://lore.kernel.org/linux-hardening/07e9bb04-f9fc-46d5-bfb9-a00a63a707c0@embeddedor.com/ On 10/24/23 13:50, Gustavo A. R. Silva wrote: > 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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