[OpenWrt-Devel] Memory leak related to OpenWrt patch of hostapd

[Nick Schaf]

Hello,
I've noticed the wpa_supplicant process on my mesh interfaces leaking memory to the point that the kernel kills the process.
It was discovered in 18.06.2, but I've reproduced it with 18.06.4 and with the master branch from the GitHub repo.  Since the leak occurs as mesh links are created and destroyed, I was able to reproduce it with a simple two-node setup where I monitor the wpa_supplicant process VSZ on one node and repeatedly bring wifi up and down on the other node.

I've traced it back to the 18.06.2 release, specifically to lines 34-35 of package/network/services/hostapd/patches/015-mesh-do-not-use-offchan-mgmt-tx-on-DFS.patch
+                 (modes = nl80211_get_hw_feature_data(bss, &num_modes, &flags,
+                                                                                             &dfs_domain)) &&
That code was added in a35f24309021c1c0e9cbed0faedf58b941cb4bd3.

I removed the entire patch file to resolve the memory leak because the subsequent call to ieee80211_is_dfs() uses the return value from nl80211_get_hw_feature_data().  However, I know the problem is specifically related to the nl80211_get_hw_feature_data() call because I stepped-backward through commits of the hostapd source until I got back to 0f7fc6b98de9c69f511b9b22f2b65553126362eb, where ieee80211_is_dfs() had only one argument and didn't rely on the nl80211_get_hw_feature_data() return value.  At that point, the memory leak still occurred until I commented-out the call to nl80211_get_hw_feature_data().

I attempted to dive into nl80211_get_hw_feature_data(), but was quickly lost, so I defer to those that are more experienced in that code.

Test platform: Compex WPJ-531 (ar71xx)

Thanks,
-Nick
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