From 11572d7d7fb9802ceb46ea9dc6cbe3bb95373e55 Mon Sep 17 00:00:00 2001 From: Mathy Vanhoef Date: Sun, 6 Jun 2021 22:10:41 +0000 Subject: [PATCH] net80211: reject mixed plaintext/encrypted fragments ieee80211_defrag() accepts fragmented 802.11 frames in a protected Wi-Fi network even when some of the fragments are not encrypted. Track whether the fragments are encrypted or not and only accept successive ones if they match the state of the first fragment. This relates to section 6.3 in the 2021 Usenix "FragAttacks" (Fragment and Forge: Breaking Wi-Fi Through Frame Aggregation and Fragmentation) paper. Submitted by: Mathy Vanhoef (Mathy.Vanhoef kuleuven.be) Security: CVE-2020-26147 PR: 256118 Differential Revision: https://reviews.freebsd.org/D30663 --- sys/net80211/ieee80211_adhoc.c | 2 +- sys/net80211/ieee80211_hostap.c | 2 +- sys/net80211/ieee80211_input.c | 21 ++++++++++++++++++--- sys/net80211/ieee80211_input.h | 2 +- sys/net80211/ieee80211_mesh.c | 2 +- sys/net80211/ieee80211_sta.c | 2 +- sys/net80211/ieee80211_wds.c | 2 +- 7 files changed, 24 insertions(+), 9 deletions(-) diff --git a/sys/net80211/ieee80211_adhoc.c b/sys/net80211/ieee80211_adhoc.c index ea1519b3381..a23f138802d 100644 --- a/sys/net80211/ieee80211_adhoc.c +++ b/sys/net80211/ieee80211_adhoc.c @@ -531,7 +531,7 @@ adhoc_input(struct ieee80211_node *ni, struct mbuf *m, * Next up, any fragmentation. */ if (!IEEE80211_IS_MULTICAST(wh->i_addr1)) { - m = ieee80211_defrag(ni, m, hdrspace); + m = ieee80211_defrag(ni, m, hdrspace, has_decrypted); if (m == NULL) { /* Fragment dropped or frame not complete yet */ goto out; diff --git a/sys/net80211/ieee80211_hostap.c b/sys/net80211/ieee80211_hostap.c index 16a3d97ae7f..15d42a68235 100644 --- a/sys/net80211/ieee80211_hostap.c +++ b/sys/net80211/ieee80211_hostap.c @@ -719,7 +719,7 @@ hostap_input(struct ieee80211_node *ni, struct mbuf *m, * Next up, any fragmentation. */ if (!IEEE80211_IS_MULTICAST(wh->i_addr1)) { - m = ieee80211_defrag(ni, m, hdrspace); + m = ieee80211_defrag(ni, m, hdrspace, has_decrypted); if (m == NULL) { /* Fragment dropped or frame not complete yet */ goto out; diff --git a/sys/net80211/ieee80211_input.c b/sys/net80211/ieee80211_input.c index aa557fc1ec2..eaeceb9d228 100644 --- a/sys/net80211/ieee80211_input.c +++ b/sys/net80211/ieee80211_input.c @@ -170,7 +170,8 @@ ieee80211_input_mimo_all(struct ieee80211com *ic, struct mbuf *m) * XXX should handle 3 concurrent reassemblies per-spec. */ struct mbuf * -ieee80211_defrag(struct ieee80211_node *ni, struct mbuf *m, int hdrspace) +ieee80211_defrag(struct ieee80211_node *ni, struct mbuf *m, int hdrspace, + int has_decrypted) { struct ieee80211vap *vap = ni->ni_vap; struct ieee80211_frame *wh = mtod(m, struct ieee80211_frame *); @@ -189,6 +190,11 @@ ieee80211_defrag(struct ieee80211_node *ni, struct mbuf *m, int hdrspace) if (!more_frag && fragno == 0 && ni->ni_rxfrag[0] == NULL) return m; + /* Temporarily set flag to remember if fragment was encrypted. */ + /* XXX use a non-packet altering storage for this in the future. */ + if (has_decrypted) + wh->i_fc[1] |= IEEE80211_FC1_PROTECTED; + /* * Remove frag to insure it doesn't get reaped by timer. */ @@ -219,10 +225,14 @@ ieee80211_defrag(struct ieee80211_node *ni, struct mbuf *m, int hdrspace) lwh = mtod(mfrag, struct ieee80211_frame *); last_rxseq = le16toh(*(uint16_t *)lwh->i_seq); - /* NB: check seq # and frag together */ + /* + * NB: check seq # and frag together. Also check that both + * fragments are plaintext or that both are encrypted. + */ if (rxseq == last_rxseq+1 && IEEE80211_ADDR_EQ(wh->i_addr1, lwh->i_addr1) && - IEEE80211_ADDR_EQ(wh->i_addr2, lwh->i_addr2)) { + IEEE80211_ADDR_EQ(wh->i_addr2, lwh->i_addr2) && + !((wh->i_fc[1] ^ lwh->i_fc[1]) & IEEE80211_FC1_PROTECTED)) { /* XXX clear MORE_FRAG bit? */ /* track last seqnum and fragno */ *(uint16_t *) lwh->i_seq = *(uint16_t *) wh->i_seq; @@ -253,6 +263,11 @@ ieee80211_defrag(struct ieee80211_node *ni, struct mbuf *m, int hdrspace) ni->ni_rxfrag[0] = mfrag; mfrag = NULL; } + /* Remember to clear protected flag that was temporarily set. */ + if (mfrag != NULL) { + wh = mtod(mfrag, struct ieee80211_frame *); + wh->i_fc[1] &= ~IEEE80211_FC1_PROTECTED; + } return mfrag; } diff --git a/sys/net80211/ieee80211_input.h b/sys/net80211/ieee80211_input.h index 7456fc68b36..61e3099cb0a 100644 --- a/sys/net80211/ieee80211_input.h +++ b/sys/net80211/ieee80211_input.h @@ -309,7 +309,7 @@ ieee80211_check_rxseq(struct ieee80211_node *ni, struct ieee80211_frame *wh, void ieee80211_deliver_data(struct ieee80211vap *, struct ieee80211_node *, struct mbuf *); struct mbuf *ieee80211_defrag(struct ieee80211_node *, - struct mbuf *, int); + struct mbuf *, int, int); struct mbuf *ieee80211_realign(struct ieee80211vap *, struct mbuf *, size_t); struct mbuf *ieee80211_decap(struct ieee80211vap *, struct mbuf *, int); struct mbuf *ieee80211_decap1(struct mbuf *, int *); diff --git a/sys/net80211/ieee80211_mesh.c b/sys/net80211/ieee80211_mesh.c index b4326905a7a..8dcbfa918e3 100644 --- a/sys/net80211/ieee80211_mesh.c +++ b/sys/net80211/ieee80211_mesh.c @@ -1641,7 +1641,7 @@ mesh_input(struct ieee80211_node *ni, struct mbuf *m, */ hdrspace = ieee80211_hdrspace(ic, wh); if (!IEEE80211_IS_MULTICAST(wh->i_addr1)) { - m = ieee80211_defrag(ni, m, hdrspace); + m = ieee80211_defrag(ni, m, hdrspace, 0); if (m == NULL) { /* Fragment dropped or frame not complete yet */ goto out; diff --git a/sys/net80211/ieee80211_sta.c b/sys/net80211/ieee80211_sta.c index 43dc8b6dfec..6d24eadc11a 100644 --- a/sys/net80211/ieee80211_sta.c +++ b/sys/net80211/ieee80211_sta.c @@ -795,7 +795,7 @@ sta_input(struct ieee80211_node *ni, struct mbuf *m, * Next up, any fragmentation. */ if (!IEEE80211_IS_MULTICAST(wh->i_addr1)) { - m = ieee80211_defrag(ni, m, hdrspace); + m = ieee80211_defrag(ni, m, hdrspace, has_decrypted); if (m == NULL) { /* Fragment dropped or frame not complete yet */ goto out; diff --git a/sys/net80211/ieee80211_wds.c b/sys/net80211/ieee80211_wds.c index 8eaffcf8773..f59a92b992d 100644 --- a/sys/net80211/ieee80211_wds.c +++ b/sys/net80211/ieee80211_wds.c @@ -594,7 +594,7 @@ wds_input(struct ieee80211_node *ni, struct mbuf *m, * Next up, any fragmentation. */ if (!IEEE80211_IS_MULTICAST(wh->i_addr1)) { - m = ieee80211_defrag(ni, m, hdrspace); + m = ieee80211_defrag(ni, m, hdrspace, has_decrypted); if (m == NULL) { /* Fragment dropped or frame not complete yet */ goto out; -- 2.45.0