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Message-ID: <abc9d7abface4b9f651fc354ebaaf30ecf6e2783.camel@redhat.com>
Date: Tue, 22 Aug 2023 12:00:17 -0500
From: Dan Williams <dcbw@...hat.com>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.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 :)
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`?
>
> 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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