[PATCH 5.10.y] wifi: mac80211: fix NULL pointer dereference in mesh_rx_csa_frame()

[Sasha Levin <sashal@kernel.org>]

From: Vahagn Vardanian <vahagn@redrays.io>

[ Upstream commit 017c1792525064a723971f0216e6ef86a8c7af11 ]

In mesh_rx_csa_frame(), elems->mesh_chansw_params_ie is dereferenced
at lines 1638 and 1642 without a prior NULL check:

    ifmsh->chsw_ttl = elems->mesh_chansw_params_ie->mesh_ttl;
    ...
    pre_value = le16_to_cpu(elems->mesh_chansw_params_ie->mesh_pre_value);

The mesh_matches_local() check above only validates the Mesh ID,
Mesh Configuration, and Supported Rates IEs.  It does not verify the
presence of the Mesh Channel Switch Parameters IE (element ID 118).
When a received CSA action frame omits that IE, ieee802_11_parse_elems()
leaves elems->mesh_chansw_params_ie as NULL, and the unconditional
dereference causes a kernel NULL pointer dereference.

A remote mesh peer with an established peer link (PLINK_ESTAB) can
trigger this by sending a crafted SPECTRUM_MGMT/CHL_SWITCH action frame
that includes a matching Mesh ID and Mesh Configuration IE but omits the
Mesh Channel Switch Parameters IE.  No authentication beyond the default
open mesh peering is required.

Crash confirmed on kernel 6.17.0-5-generic via mac80211_hwsim:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  Oops: Oops: 0000 [#1] SMP NOPTI
  RIP: 0010:ieee80211_mesh_rx_queued_mgmt+0x143/0x2a0 [mac80211]
  CR2: 0000000000000000

Fix by adding a NULL check for mesh_chansw_params_ie after
mesh_matches_local() returns, consistent with how other optional IEs
are guarded throughout the mesh code.

The bug has been present since v3.13 (released 2014-01-19).

Fixes: 8f2535b92d68 ("mac80211: process the CSA frame for mesh accordingly")
Cc: stable@vger.kernel.org
Signed-off-by: Vahagn Vardanian <vahagn@redrays.io>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
[ adapted pointer access elems-> to stack struct elems, and replaced goto free with return ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/mac80211/mesh.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mac80211/mesh.c b/net/mac80211/mesh.c
index d3a9ce1f8e53f..20b8ff83e3dbd 100644
--- a/net/mac80211/mesh.c
+++ b/net/mac80211/mesh.c
@@ -1435,6 +1435,9 @@ static void mesh_rx_csa_frame(struct ieee80211_sub_if_data *sdata,
 	if (!mesh_matches_local(sdata, &elems))
 		return;
 
+	if (!elems.mesh_chansw_params_ie)
+		return;
+
 	ifmsh->chsw_ttl = elems.mesh_chansw_params_ie->mesh_ttl;
 	if (!--ifmsh->chsw_ttl)
 		fwd_csa = false;
-- 
2.51.0