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Date: Tue, 22 Aug 2023 13:23:39 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Dan Williams <dcbw@...hat.com>,
Brian Norris <briannorris@...omium.org>,
Kalle Valo <kvalo@...nel.org>
Cc: 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] wifi: mwifiex: Asking for some light on this, please :)
Hi Dan,
Thanks a lot for the feedback!
Please, see my comments below.
On 8/22/23 11:00, Dan Williams wrote:
> On Tue, 2023-08-15 at 18:52 -0600, Gustavo A. R. Silva wrote:
>> Hi all,
>>
>> While working on flex-array transformations I ran into the following
>> implementation:
>>
>> drivers/net/wireless/marvell/mwifiex/fw.h:775:
>> struct mwifiex_ie_types_rxba_sync {
>> struct mwifiex_ie_types_header header;
>> u8 mac[ETH_ALEN];
>> u8 tid;
>> u8 reserved;
>> __le16 seq_num;
>> __le16 bitmap_len;
>> u8 bitmap[1];
>> } __packed;
>>
>> `bitmap` is currently being used as a fake-flex array and we should
>> transform it into a proper flexible-array member.
>>
>> However, while doing that, I noticed something in the following function
>> that's not clear to me and I wanted to ask you for feedback:
>>
>> drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c:907:
>> void mwifiex_11n_rxba_sync_event(struct mwifiex_private *priv,
>> u8 *event_buf, u16 len)
>> {
>> struct mwifiex_ie_types_rxba_sync *tlv_rxba = (void *)event_buf;
>> u16 tlv_type, tlv_len;
>> struct mwifiex_rx_reorder_tbl *rx_reor_tbl_ptr;
>> u8 i, j;
>> u16 seq_num, tlv_seq_num, tlv_bitmap_len;
>> int tlv_buf_left = len;
>> int ret;
>> u8 *tmp;
>>
>> mwifiex_dbg_dump(priv->adapter, EVT_D, "RXBA_SYNC event:",
>> event_buf, len);
>> while (tlv_buf_left >= sizeof(*tlv_rxba)) {
>
>> tlv_type = le16_to_cpu(tlv_rxba->header.type);
>> tlv_len = le16_to_cpu(tlv_rxba->header.len);
>
>> if (tlv_type != TLV_TYPE_RXBA_SYNC) {
>> mwifiex_dbg(priv->adapter, ERROR,
>> "Wrong TLV id=0x%x\n", tlv_type);
>> return;
>> }
>>
>> tlv_seq_num = le16_to_cpu(tlv_rxba->seq_num);
>> tlv_bitmap_len = le16_to_cpu(tlv_rxba->bitmap_len);
>
> This seems superfluous since couldn't the bitmap_len be calculated from
> the tlv_len and sizeof(*tlv_rxba)? But whatever, sure.
>
> Seems like there should be some input validation here to ensure that
> tlv_bitmap_len and tlv_len don't overrun event_buf's memory though, if
> the firmware is hosed or malicious.
>
> But that's not your problem since you're not touching this code.
>
>> mwifiex_dbg(priv->adapter, INFO,
>> "%pM tid=%d seq_num=%d bitmap_len=%d\n",
>> tlv_rxba->mac, tlv_rxba->tid, tlv_seq_num,
>> tlv_bitmap_len);
>>
>> rx_reor_tbl_ptr =
>> mwifiex_11n_get_rx_reorder_tbl(priv, tlv_rxba->tid,
>> tlv_rxba->mac);
>> if (!rx_reor_tbl_ptr) {
>> mwifiex_dbg(priv->adapter, ERROR,
>> "Can not find rx_reorder_tbl!");
>> return;
>> }
>>
>> for (i = 0; i < tlv_bitmap_len; i++) {
>> for (j = 0 ; j < 8; j++) {
>> if (tlv_rxba->bitmap[i] & (1 << j)) {
>> seq_num = (MAX_TID_VALUE - 1) &
>> (tlv_seq_num + i * 8 + j);
>>
>> mwifiex_dbg(priv->adapter, ERROR,
>> "drop packet,seq=%d\n",
>> seq_num);
>>
>> ret = mwifiex_11n_rx_reorder_pkt
>> (priv, seq_num, tlv_rxba->tid,
>> tlv_rxba->mac, 0, NULL);
>>
>> if (ret)
>> mwifiex_dbg(priv->adapter,
>> ERROR,
>> "Fail to drop packet");
>> }
>> }
>> }
>>
>> tlv_buf_left -= (sizeof(*tlv_rxba) + tlv_len);
>
> Now we have to subtract the size of the whole TLV (including the header
> and flexarray) from the remaining bytes in event_buf.
>
> But this looks pretty sketchy. Marvell TLVs have a header (the TL of
> the TLV) and header->len says how long the V is. Most Marvell kernel
> driver code (mwifiex, libertas, etc) does something like this:
>
> pos += ssid_tlv->header + ssid_tlv->header.len;
>
> but tlv_rxba is much more than just the header; I think this code is
> going to *over* count how many bytes were just consumed.
>
> I'm not the only one thinking it's sketchy:
>
> https://www.spinics.net/lists/linux-wireless/msg174231.html
>
>> tmp = (u8 *)tlv_rxba + tlv_len + sizeof(*tlv_rxba);
>>
>> What's the relation between tlv_len, sizeof(*tlv_rxba) and tlv_bitmap_len?
>>
>> Isn't `sizeof(*tlv_rxba) + tlv_len` and `tlv_len + sizeof(*tlv_rxba)`
>> double-counting some fields in `struct mwifiex_ie_types_rxba_sync`?
OK. So, based on your feedback, it seems that my assumptions were correct.
So, first I'll send the following fix:
diff --git a/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c b/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
index 391793a16adc..9eade3aa2918 100644
--- a/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
+++ b/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
@@ -965,8 +965,8 @@ void mwifiex_11n_rxba_sync_event(struct mwifiex_private *priv,
}
}
- tlv_buf_left -= (sizeof(*tlv_rxba) + tlv_len);
- tmp = (u8 *)tlv_rxba + tlv_len + sizeof(*tlv_rxba);
+ tlv_buf_left -= (sizeof(tlv_rxba->header) + tlv_len);
+ tmp = (u8 *)tlv_rxba + tlv_len + sizeof(tlv_rxba->header);
tlv_rxba = (struct mwifiex_ie_types_rxba_sync *)tmp;
}
}
Then, I'll do the flex-array transformation on top of the fix above:
diff --git a/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c b/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
index 9eade3aa2918..cb5a399cd56a 100644
--- a/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
+++ b/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
@@ -918,7 +918,7 @@ void mwifiex_11n_rxba_sync_event(struct mwifiex_private *priv,
mwifiex_dbg_dump(priv->adapter, EVT_D, "RXBA_SYNC event:",
event_buf, len);
- while (tlv_buf_left >= sizeof(*tlv_rxba)) {
+ while (tlv_buf_left > sizeof(*tlv_rxba)) {
tlv_type = le16_to_cpu(tlv_rxba->header.type);
tlv_len = le16_to_cpu(tlv_rxba->header.len);
if (tlv_type != TLV_TYPE_RXBA_SYNC) {
diff --git a/drivers/net/wireless/marvell/mwifiex/fw.h b/drivers/net/wireless/marvell/mwifiex/fw.h
index f2168fac95ed..8e6db904e5b2 100644
--- a/drivers/net/wireless/marvell/mwifiex/fw.h
+++ b/drivers/net/wireless/marvell/mwifiex/fw.h
@@ -779,7 +779,7 @@ struct mwifiex_ie_types_rxba_sync {
u8 reserved;
__le16 seq_num;
__le16 bitmap_len;
- u8 bitmap[1];
+ u8 bitmap[];
} __packed;
struct chan_band_param_set {
This happilly results in no binary output differences before/after changes. :)
Finally, to top it off, I can send this sanity check:
diff --git a/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c b/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
index cb5a399cd56a..237d0ee3573f 100644
--- a/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
+++ b/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
@@ -929,6 +929,13 @@ void mwifiex_11n_rxba_sync_event(struct mwifiex_private *priv,
tlv_seq_num = le16_to_cpu(tlv_rxba->seq_num);
tlv_bitmap_len = le16_to_cpu(tlv_rxba->bitmap_len);
+ if (sizeof(*tlv_rxba) + tlv_bitmap_len > tlv_buf_left) {
+ mwifiex_dbg(priv->adapter, ERROR,
+ "TLV size (%ld) overflows event_buf (%d)\n",
+ sizeof(*tlv_rxba) + tlv_bitmap_len,
+ tlv_buf_left);
+ return;
+ }
mwifiex_dbg(priv->adapter, INFO,
"%pM tid=%d seq_num=%d bitmap_len=%d\n",
tlv_rxba->mac, tlv_rxba->tid, tlv_seq_num,
I wanted to used `sizeof(*tlv_rxba) + tlv_bitmap_len` here instead of
`sizeof(tlv_rxba->header) + tlv_len` to avoid any issues in case there
is any (buggy) discrepancy between `tlv_len` and `tlv_bitmap_len`.
This is when for some (weird) reason
`tlv_len - (sizeof(*tlv_rxba) - sizeof(tlv_rxba->header)) != tlv_bitmap_len`
What do you think?
Thanks!
--
Gustavo
>>
>> Shouldn't this be something like this, instead (before the flex-array
>> transformation, of course):
>>
>> - tlv_buf_left -= (sizeof(*tlv_rxba) + tlv_len);
>> - tmp = (u8 *)tlv_rxba + tlv_len + sizeof(*tlv_rxba);
>> + tlv_buf_left -= (sizeof(*tlv_rxba) + tlv_bitmap_len - 1);
>> + tmp = (u8 *)tlv_rxba + tlv_bitmap_len + sizeof(*tlv_rxba - 1);
>
> If my assertion about tlv->header.len is correct then we can do:
>
> tlv_buf_left -= sizeof(tlv_rxba->header) + tlv_len;
> tmp = (u8 *)tlv_rxba + sizeof(tlv_rxba->header) + tlv_len;
>
>>
>>
>> tlv_rxba = (struct mwifiex_ie_types_rxba_sync *)tmp;
>
> This is silly; instead of tmp we could do:
>
> u16 bytes_used;
>
> ...
>
> bytes_used = sizeof(tlv_rxba->header) + tlv_len;
> tlv_buf_left -= bytes_used;
> tlv_rxba += bytes_used;
>
> (with appropriate casting).
>
> Dan
>
>> }
>> }
>>
>> Thanks in advance for any feedback!
>>
>> --
>> Gustavo
>>
>
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