Messages in this thread Patch in this message | | | Date | Tue, 24 Oct 2023 14:41:07 -0600 | Subject | Re: [RFC - is this a bug?] wifi: ath10k: Asking for some light on this, please :) | From | "Gustavo A. R. Silva" <> |
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On 10/24/23 14:11, Johannes Berg wrote: > On Tue, 2023-10-24 at 13:50 -0600, 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: > > >> 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? >> > > If we look a step further, I _think_ even that memset is unnecessary?
It seems we run into the same issue in the function below, even in the case this `memset()` is unnecessary (which it seems it's not):
8920 memset(skb->data, 0, sizeof(*cmd));
Notice that if `cap->peer_chan_len == 0` or `cap->peer_chan_len == 1`, in the original code, we have `len == sizeof(*cmd) == 128`:
drivers/net/wireless/ath/ath10k/wmi.c: 8911 /* tdls peer update cmd has place holder for one channel*/ 8912 chan_len = cap->peer_chan_len ? (cap->peer_chan_len - 1) : 0; 8913 8914 len = sizeof(*cmd) + chan_len * sizeof(*chan); 8915 8916 skb = ath10k_wmi_alloc_skb(ar, len);
> > > struct sk_buff *ath10k_wmi_alloc_skb(struct ath10k *ar, u32 len) > { > struct sk_buff *skb; > u32 round_len = roundup(len, 4); > > skb = ath10k_htc_alloc_skb(ar, WMI_SKB_HEADROOM + round_len); > if (!skb) > return NULL; > > skb_reserve(skb, WMI_SKB_HEADROOM); > if (!IS_ALIGNED((unsigned long)skb->data, 4)) > ath10k_warn(ar, "Unaligned WMI skb\n"); > > skb_put(skb, round_len);
so `round_len == roundup(len, 4) == 128` at the moment of this `memset()` call:
> memset(skb->data, 0, round_len);
which take us back to the same problem, this time in the `memset()` above, because after the flex-array transformation we would have:
--- a/drivers/net/wireless/ath/ath10k/wmi.c +++ b/drivers/net/wireless/ath/ath10k/wmi.c @@ -8905,13 +8905,10 @@ ath10k_wmi_10_4_gen_tdls_peer_update(struct ath10k *ar, struct wmi_channel *chan; struct sk_buff *skb; u32 peer_qos; - int len, chan_len; + size_t len; int i;
- /* tdls peer update cmd has place holder for one channel*/ - chan_len = cap->peer_chan_len ? (cap->peer_chan_len - 1) : 0; - - len = sizeof(*cmd) + chan_len * sizeof(*chan); + len = struct_size(cmd, peer_capab.peer_chan_list, cap->peer_chan_len);
skb = ath10k_wmi_alloc_skb(ar, len); if (!skb) which makes `round_len == roundup(len, 4) == struct_size(cmd,...,...) == 104` when `cap->peer_chan_len == 0`
> So shouldn't the outgoing skb be exactly the same?
It seems it's not.
> > Anyway, just looking at the code out of curiosity, I don't actually know > anything about this driver :) > > johannes
-- Gustavo
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