Re: [PATCH 02/64] mac80211: Use flex-array for radiotap header bitmap

Dan Carpenter
2021-07-28T07:36:39Z

On Tue, Jul 27, 2021 at 01:57:53PM -0700, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally writing across neighboring fields.
>
> The it_present member of struct ieee80211_radiotap_header is treated as a
> flexible array (multiple u32s can be conditionally present). In order for
> memcpy() to reason (or really, not reason) about the size of operations
> against this struct, use of bytes beyond it_present need to be treated
> as part of the flexible array. Add a union/struct to contain the new
> "bitmap" member, for use with trailing presence bitmaps and arguments.
>
> Additionally improve readability in the iterator code which walks
> through the bitmaps and arguments.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> include/net/ieee80211_radiotap.h | 24 ++++++++++++++++++++----
> net/mac80211/rx.c | 2 +-
> net/wireless/radiotap.c | 5 ++---
> 3 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/include/net/ieee80211_radiotap.h b/include/net/ieee80211_radiotap.h
> index c0854933e24f..101c1e961032 100644
> --- a/include/net/ieee80211_radiotap.h
> +++ b/include/net/ieee80211_radiotap.h
> @@ -39,10 +39,26 @@ struct ieee80211_radiotap_header {
> */
> __le16 it_len;
>
> - /**
> - * @it_present: (first) present word
> - */
> - __le32 it_present;
> + union {
> + /**
> + * @it_present: (first) present word
> + */
> + __le32 it_present;
> +
> + struct {
> + /* The compiler makes it difficult to overlap
> + * a flex-array with an existing singleton,
> + * so we're forced to add an empty named
> + * variable here.
> + */
> + struct { } __unused;
> +
> + /**
> + * @bitmap: all presence bitmaps
> + */
> + __le32 bitmap[];
> + };
> + };
> } __packed;

This patch is so confusing...

Btw, after the end of the __le32 data there is a bunch of other le64,
u8 and le16 data so the struct is not accurate or complete.

It might be better to re-write this as something like this:

diff --git a/include/net/ieee80211_radiotap.h b/include/net/ieee80211_radiotap.h
index c0854933e24f..0cb5719e9668 100644
--- a/include/net/ieee80211_radiotap.h
+++ b/include/net/ieee80211_radiotap.h
@@ -42,7 +42,10 @@ struct ieee80211_radiotap_header {
/**
* @it_present: (first) present word
*/
- __le32 it_present;
+ struct {
+ __le32 it_present;
+ char buff[];
+ } data;
} __packed;

/* version is always 0 */
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 771921c057e8..9cc891364a07 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -328,7 +328,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,

rthdr = skb_push(skb, rtap_len);
memset(rthdr, 0, rtap_len - rtap.len - rtap.pad);
- it_present = &rthdr->it_present;
+ it_present = (__le32 *)&rthdr->data;

/* radiotap header, set always present flags */
rthdr->it_len = cpu_to_le16(rtap_len);
@@ -372,7 +372,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
ieee80211_calculate_rx_timestamp(local, status,
mpdulen, 0),
pos);
- rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_TSFT);
+ rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_TSFT);
pos += 8;
}

@@ -396,7 +396,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
*pos = 0;
} else {
int shift = 0;
- rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_RATE);
+ rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_RATE);
if (status->bw == RATE_INFO_BW_10)
shift = 1;
else if (status->bw == RATE_INFO_BW_5)
@@ -432,7 +432,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
if (ieee80211_hw_check(&local->hw, SIGNAL_DBM) &&
!(status->flag & RX_FLAG_NO_SIGNAL_VAL)) {
*pos = status->signal;
- rthdr->it_present |=
+ rthdr->data.it_present |=
cpu_to_le32(1 << IEEE80211_RADIOTAP_DBM_ANTSIGNAL);
pos++;
}
@@ -459,7 +459,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
if (status->encoding == RX_ENC_HT) {
unsigned int stbc;

- rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_MCS);
+ rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_MCS);
*pos++ = local->hw.radiotap_mcs_details;
*pos = 0;
if (status->enc_flags & RX_ENC_FLAG_SHORT_GI)
@@ -482,7 +482,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
/* ensure 4 byte alignment */
while ((pos - (u8 *)rthdr) & 3)
pos++;
- rthdr->it_present |=
+ rthdr->data.it_present |=
cpu_to_le32(1 << IEEE80211_RADIOTAP_AMPDU_STATUS);
put_unaligned_le32(status->ampdu_reference, pos);
pos += 4;
@@ -510,7 +510,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
if (status->encoding == RX_ENC_VHT) {
u16 known = local->hw.radiotap_vht_details;

- rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_VHT);
+ rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_VHT);
put_unaligned_le16(known, pos);
pos += 2;
/* flags */
@@ -553,7 +553,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
u16 accuracy = 0;
u8 flags = IEEE80211_RADIOTAP_TIMESTAMP_FLAG_32BIT;

- rthdr->it_present |=
+ rthdr->data.it_present |=
cpu_to_le32(1 << IEEE80211_RADIOTAP_TIMESTAMP);

/* ensure 8 byte alignment */
@@ -642,7 +642,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
/* ensure 2 byte alignment */
while ((pos - (u8 *)rthdr) & 1)
pos++;
- rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_HE);
+ rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_HE);
memcpy(pos, &he, sizeof(he));
pos += sizeof(he);
}
@@ -652,13 +652,13 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
/* ensure 2 byte alignment */
while ((pos - (u8 *)rthdr) & 1)
pos++;
- rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_HE_MU);
+ rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_HE_MU);
memcpy(pos, &he_mu, sizeof(he_mu));
pos += sizeof(he_mu);
}

if (status->flag & RX_FLAG_NO_PSDU) {
- rthdr->it_present |=
+ rthdr->data.it_present |=
cpu_to_le32(1 << IEEE80211_RADIOTAP_ZERO_LEN_PSDU);
*pos++ = status->zero_length_psdu_type;
}
@@ -667,7 +667,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
/* ensure 2 byte alignment */
while ((pos - (u8 *)rthdr) & 1)
pos++;
- rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_LSIG);
+ rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_LSIG);
memcpy(pos, &lsig, sizeof(lsig));
pos += sizeof(lsig);
}
diff --git a/net/wireless/radiotap.c b/net/wireless/radiotap.c
index 36f1b59a78bf..f7852024c011 100644
--- a/net/wireless/radiotap.c
+++ b/net/wireless/radiotap.c
@@ -114,11 +114,10 @@ int ieee80211_radiotap_iterator_init(
iterator->_rtheader = radiotap_header;
iterator->_max_length = get_unaligned_le16(&radiotap_header->it_len);
iterator->_arg_index = 0;
- iterator->_bitmap_shifter = get_unaligned_le32(&radiotap_header->it_present);
+ iterator->_bitmap_shifter = get_unaligned_le32(&radiotap_header->data.it_present);
iterator->_arg = (uint8_t *)radiotap_header + sizeof(*radiotap_header);
iterator->_reset_on_ext = 0;
- iterator->_next_bitmap = &radiotap_header->it_present;
- iterator->_next_bitmap++;
+ iterator->_next_bitmap = (__le32 *)&radiotap_header->data.buff;
iterator->_vns = vns;
iterator->current_namespace = &radiotap_ns;
iterator->is_radiotap_ns = 1;