[v2] wifi: mac80211: fix integer overflow in hwmp_route_info_get()

Commit Message

Gavrilov Ilia Jan. 16, 2025, 8:31 a.m. UTC

Since the new_metric and last_hop_metric variables can reach
the MAX_METRIC(0xffffffff) value, an integer overflow may occur
when multiplying them by 10/9. It can lead to incorrect behavior.

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with SVACE.

Fixes: a8d418d9ac25 ("mac80211: mesh: only switch path when new metric is at least 10% better")
Cc: [e-mail]
Signed-off-by: Ilia Gavrilov <[e-mail]>
---
v2:
- Remove 64-bit arithmetic according to https://lore.kernel.org/all/[e-mail]/
- Replace multiplication by 10/9 with a function that compares metrics by adding 10% without integer overflow
 net/mac80211/mesh_hwmp.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

Patch

diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c
index 4e9546e998b6..4a7446e4c226 100644
--- a/net/mac80211/mesh_hwmp.c
+++ b/net/mac80211/mesh_hwmp.c
@@ -367,6 +367,26 @@  u32 airtime_link_metric_get(struct ieee80211_local *local,
 	return (u32)result;
 }
 
+static inline bool is_metric_better(u32 x, u32 y, u32 persent)
+{
+	u32 a, e;
+
+	if (x >= y)
+		return false;
+
+	a = mult_frac(x, persent, 100);
+
+	if (check_add_overflow(x, a, &e)) {
+		if (x > y - a)
+			return false;
+	} else {
+		if (e > y)
+			return false;
+	}
+
+	return true;
+}
+
 /**
  * hwmp_route_info_get - Update routing info to originator and transmitter
  *
@@ -458,8 +478,8 @@  static u32 hwmp_route_info_get(struct ieee80211_sub_if_data *sdata,
 				    (mpath->sn == orig_sn &&
 				     (rcu_access_pointer(mpath->next_hop) !=
 						      sta ?
-					      mult_frac(new_metric, 10, 9) :
-					      new_metric) >= mpath->metric)) {
+					      !is_metric_better(new_metric, mpath->metric, 10) :
+					      new_metric >= mpath->metric))) {
 					process = false;
 					fresh_info = false;
 				}
@@ -533,8 +553,8 @@  static u32 hwmp_route_info_get(struct ieee80211_sub_if_data *sdata,
 			if ((mpath->flags & MESH_PATH_FIXED) ||
 			    ((mpath->flags & MESH_PATH_ACTIVE) &&
 			     ((rcu_access_pointer(mpath->next_hop) != sta ?
-				       mult_frac(last_hop_metric, 10, 9) :
-				       last_hop_metric) > mpath->metric)))
+				      !is_metric_better(last_hop_metric, mpath->metric, 10) :
+				       last_hop_metric > mpath->metric))))
 				fresh_info = false;
 		} else {
 			mpath = mesh_path_add(sdata, ta);