nl80211: prefer struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the struct_size() helper to do the arithmetic instead of the
argument "size + count * size" in the kzalloc() functions.

Also, take the opportunity to refactor the memcpy() call to use the
flex_array_size() helper.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@gmx.com>
Link: https://lore.kernel.org/r/20210919114040.41522-1-len.baker@gmx.com
[remove unnecessary variable]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index bf7cd47..e4787c7 100644 (file)
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -11767,8 +11767,9 @@ static int nl80211_set_cqm_rssi(struct genl_info *info,
        if (n_thresholds) {
                struct cfg80211_cqm_config *cqm_config;
 
-               cqm_config = kzalloc(sizeof(struct cfg80211_cqm_config) +
-                                    n_thresholds * sizeof(s32), GFP_KERNEL);
+               cqm_config = kzalloc(struct_size(cqm_config, rssi_thresholds,
+                                                n_thresholds),
+                                    GFP_KERNEL);
                if (!cqm_config) {
                        err = -ENOMEM;
                        goto unlock;
@@ -11777,7 +11778,8 @@ static int nl80211_set_cqm_rssi(struct genl_info *info,
                cqm_config->rssi_hyst = hysteresis;
                cqm_config->n_rssi_thresholds = n_thresholds;
                memcpy(cqm_config->rssi_thresholds, thresholds,
-                      n_thresholds * sizeof(s32));
+                      flex_array_size(cqm_config, rssi_thresholds,
+                                      n_thresholds));
 
                wdev->cqm_config = cqm_config;
        }
@@ -15081,9 +15083,7 @@ static int nl80211_set_sar_specs(struct sk_buff *skb, struct genl_info *info)
        if (specs > rdev->wiphy.sar_capa->num_freq_ranges)
                return -EINVAL;
 
-       sar_spec = kzalloc(sizeof(*sar_spec) +
-                          specs * sizeof(struct cfg80211_sar_sub_specs),
-                          GFP_KERNEL);
+       sar_spec = kzalloc(struct_size(sar_spec, sub_specs, specs), GFP_KERNEL);
        if (!sar_spec)
                return -ENOMEM;