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
