[PATCH AUTOSEL 6.6 07/62] wifi: mt76: mt7996: drop fragments with multicast or broadcast RA

[Sasha Levin]

From: Benjamin Lin <benjamin-jw.lin at mediatek.com>

[ Upstream commit 80fda1cd7b0a1edd0849dc71403a070d0922118d ]

IEEE 802.11 fragmentation can only be applied to unicast frames.
Therefore, drop fragments with multicast or broadcast RA. This patch
addresses vulnerabilities such as CVE-2020-26145.

Signed-off-by: Benjamin Lin <benjamin-jw.lin at mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen at mediatek.com>
Link: https://patch.msgid.link/20250515032952.1653494-4-shayne.chen@mediatek.com
Signed-off-by: Felix Fietkau <nbd at nbd.name>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---

## Analysis Complete **YES** This commit should be backported to stable
kernel trees. Here's my extensive analysis: ### Security Fix for Known
CVE The commit directly addresses **CVE-2020-26145**, a documented
security vulnerability related to improper handling of fragmented frames
with multicast/broadcast addresses. This is explicitly mentioned in the
commit message and code comments. ### Code Analysis The change adds a
critical security check in
`drivers/net/wireless/mediatek/mt76/mt7996/mac.c` in the
`mt7996_mac_fill_rx()` function: ```c /bin /bin.usr-is-merged /boot /dev
/etc /home /init /lib /lib.usr-is-merged /lib64 /lost+found /media /mnt
/opt /proc /root /run /sbin /sbin.usr-is-merged /snap /srv /sys /tmp
/usr /var IEEE 802.11 fragmentation can only be applied to unicast
frames. linux Hence, drop fragments with multicast/broadcast RA. linux
This check fixes vulnerabilities, like CVE-2020-26145. linux/ if
((ieee80211_has_morefrags(fc) || seq_ctrl & IEEE80211_SCTL_FRAG) &&
FIELD_GET(MT_RXD3_NORMAL_ADDR_TYPE, rxd3) != MT_RXD3_NORMAL_U2M) return
-EINVAL; ``` The logic checks: 1. **Fragment detection**:
`ieee80211_has_morefrags(fc)` detects if there are more fragments, and
`seq_ctrl & IEEE80211_SCTL_FRAG` checks the fragment number field 2.
**Address type filtering**: `FIELD_GET(MT_RXD3_NORMAL_ADDR_TYPE, rxd3)
!= MT_RXD3_NORMAL_U2M` ensures only unicast-to-multicast (U2M) frames
are allowed when fragmented ### Comparison with Similar Commits Looking
at the historical examples: **Similar Backported Commits (Status:
YES):** - ath10k commits dropping multicast fragments (both PCIe and
SDIO versions) for the same CVE-2020-26145 - mt7915 fragmentation
threshold dummy implementation **Pattern Match:** This commit follows
the exact same pattern as the successfully backported ath10k commits
that address CVE-2020-26145 by dropping fragmented frames with
multicast/broadcast destination addresses. ### Risk Assessment **Low
Risk:** - **Small, contained change**: Only 4 lines of code added -
**Early validation**: Check happens early in the RX path before frame
processing - **Conservative approach**: Drops potentially malicious
frames rather than processing them - **No architectural changes**:
Doesn't modify existing data structures or interfaces - **Clear error
path**: Returns `-EINVAL` which is a standard error handling pattern in
this codebase **High Security Benefit:** - Addresses a known CVE
affecting wireless security - Prevents potential exploitation through
malformed fragmented multicast frames - Aligns with IEEE 802.11 standard
(fragmentation only for unicast) ### Subsystem Stability The mt7996
driver is part of the MediaTek mt76 wireless driver family, and similar
security fixes have been successfully backported to other drivers in
this family without issues. ### Conclusion This is a textbook example of
a commit that should be backported: it's a small, low-risk security fix
for a documented CVE, follows established patterns from other successful
backports, and provides important protection against a wireless security
vulnerability.

 drivers/net/wireless/mediatek/mt76/mt7996/mac.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
index 73d46ec1181ae..c55b3e621bc0e 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
@@ -650,6 +650,14 @@ mt7996_mac_fill_rx(struct mt7996_dev *dev, struct sk_buff *skb)
 		status->last_amsdu = amsdu_info == MT_RXD4_LAST_AMSDU_FRAME;
 	}
 
+	/* IEEE 802.11 fragmentation can only be applied to unicast frames.
+	 * Hence, drop fragments with multicast/broadcast RA.
+	 * This check fixes vulnerabilities, like CVE-2020-26145.
+	 */
+	if ((ieee80211_has_morefrags(fc) || seq_ctrl & IEEE80211_SCTL_FRAG) &&
+	    FIELD_GET(MT_RXD3_NORMAL_ADDR_TYPE, rxd3) != MT_RXD3_NORMAL_U2M)
+		return -EINVAL;
+
 	hdr_gap = (u8 *)rxd - skb->data + 2 * remove_pad;
 	if (hdr_trans && ieee80211_has_morefrags(fc)) {
 		if (mt7996_reverse_frag0_hdr_trans(skb, hdr_gap))
-- 
2.39.5