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
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?
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);
memset(skb->data, 0, round_len);
return skb;
}
So shouldn't the outgoing skb be exactly the same?
Anyway, just looking at the code out of curiosity, I don't actually know
anything about this driver :)
johannes
On Tue, 2023-10-24 at 14:41 -0600, Gustavo A. R. Silva wrote:
>
> 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`:
Right.
> - /* 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`
And yeah, that's really the issue, it only matters for ==0. For a moment
there I thought that doesn't even make sense, but it looks like it never
even becomes non-zero.
No idea then, sorry. You'd hope firmware doesn't care about the actual
message size if the inner data says "0 entries", but who knows? And how
many firmware versions are there? :)
So I guess you'd want to stay compatible, even if it means having a
chan_len = min(cap->peer_chan_len, 1);
for the struct_size()?
johannes
[+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/[email protected]/
[2] https://lore.kernel.org/linux-hardening/[email protected]/
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
>
>
On 10/25/2023 8:52 AM, Jeff Johnson wrote:
> On 10/24/2023 7:37 PM, Gustavo A. R. Silva wrote:
>>
>>
>> On 10/24/23 14:49, Johannes Berg wrote:
>>> On Tue, 2023-10-24 at 14:41 -0600, Gustavo A. R. Silva wrote:
>>>>
>>>> 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`:
>>>
>>> Right.
>>>
>>>> - /* 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`
>>>
>>> And yeah, that's really the issue, it only matters for ==0. For a moment
>>> there I thought that doesn't even make sense, but it looks like it never
>>> even becomes non-zero.
>>>
>>> No idea then, sorry. You'd hope firmware doesn't care about the actual
>>> message size if the inner data says "0 entries", but who knows? And how
>>> many firmware versions are there? :)
>>>
>>> So I guess you'd want to stay compatible, even if it means having a
>>>
>>> chan_len = min(cap->peer_chan_len, 1);
>>>
>>> for the struct_size()?
>>
>> Yeah, that's an alternative.
>>
>> I'll wait for the maintainers to chime in and see if they have a different
>> opinion.
>
> I'm seeing clarification from the development team.
>
> /jeff
>
I was not able to get a response from the firmware team.
I have gone ahead and created a series of patches to fix the remaining
flexible array issues in ath10k including the one discussed here. I
should be able to post those sometime this week.
/jeff