[PATCH] mac80211: Recast pointer for trailing memcpy()

[PATCH] mac80211: Recast pointer for trailing memcpy()

[Kees Cook]

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring array fields.

Give memcpy() a specific source pointer type so it can correctly
calculate the bounds of the copy.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 net/mac80211/rx.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index af0ef456eb0f..cb141bb788a8 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -559,6 +559,8 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
 
 	if (status->encoding == RX_ENC_HE &&
 	    status->flag & RX_FLAG_RADIOTAP_HE) {
+		struct ieee80211_radiotap_he *he_ptr;
+
 #define HE_PREP(f, val)	le16_encode_bits(val, IEEE80211_RADIOTAP_HE_##f)
 
 		if (status->enc_flags & RX_ENC_FLAG_STBC_MASK) {
@@ -626,18 +628,22 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
 		while ((pos - (u8 *)rthdr) & 1)
 			pos++;
 		rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_HE);
-		memcpy(pos, &he, sizeof(he));
-		pos += sizeof(he);
+		he_ptr = (void *)pos;
+		memcpy(he_ptr, &he, sizeof(he));
+		pos += sizeof(*he_ptr);
 	}
 
 	if (status->encoding == RX_ENC_HE &&
 	    status->flag & RX_FLAG_RADIOTAP_HE_MU) {
+		struct ieee80211_radiotap_he_mu *he_mu_ptr;
+
 		/* ensure 2 byte alignment */
 		while ((pos - (u8 *)rthdr) & 1)
 			pos++;
 		rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_HE_MU);
-		memcpy(pos, &he_mu, sizeof(he_mu));
-		pos += sizeof(he_mu);
+		he_mu_ptr = (void *)pos;
+		memcpy(he_mu_ptr, &he_mu, sizeof(he_mu));
+		pos += sizeof(*he_mu_ptr);
 	}
 
 	if (status->flag & RX_FLAG_NO_PSDU) {
@@ -647,12 +653,14 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
 	}
 
 	if (status->flag & RX_FLAG_RADIOTAP_LSIG) {
+		struct ieee80211_radiotap_lsig *lsig_ptr;
 		/* ensure 2 byte alignment */
 		while ((pos - (u8 *)rthdr) & 1)
 			pos++;
 		rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_LSIG);
-		memcpy(pos, &lsig, sizeof(lsig));
-		pos += sizeof(lsig);
+		lsig_ptr = (void *)pos;
+		memcpy(lsig_ptr, &lsig, sizeof(lsig));
+		pos += sizeof(*lsig_ptr);
 	}
 
 	for_each_set_bit(chain, &chains, IEEE80211_MAX_CHAINS) {
-- 
2.25.1

Re: [PATCH] mac80211: Recast pointer for trailing memcpy()

[Kees Cook]

On Wed, Jun 16, 2021 at 09:27:09PM -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 array fields.
> 
> Give memcpy() a specific source pointer type so it can correctly
> calculate the bounds of the copy.

Hmpf, please ignore this patch; sorry for the noise. This fix got
mis-tested on my end and does not solve the problem I was trying to solve.
I will return with a v2. :)

-- 
Kees Cook

RE: [PATCH] mac80211: Recast pointer for trailing memcpy()

[David Laight]

From: Kees Cook
> Sent: 17 June 2021 05:27
> 
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally writing across neighboring array fields.
> 
> Give memcpy() a specific source pointer type so it can correctly
> calculate the bounds of the copy.

Doesn't the necessity of this sort of patch just sidestep the
run-time checking and really indicate that it is just a complete
waste of cpu resources?

I bet code changes to avoid/fix the reported errors will
introduce more bugs than the test itself will really find.

	David

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