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FS#3045 - In kernel WiFi pcap filters filter too much #7816

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openwrt-bot opened this issue Apr 25, 2020 · 4 comments
Open

FS#3045 - In kernel WiFi pcap filters filter too much #7816

openwrt-bot opened this issue Apr 25, 2020 · 4 comments
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flyspray kernel pull request/issue with Linux kernel related changes release/19.07 pull request/issue targeted (also) for OpenWrt 19.07 release

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@openwrt-bot
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RedDwarf:

In an Archer C7 just flashed with https://downloads.openwrt.org/releases/19.07.2/targets/ath79/generic/openwrt-19.07.2-ath79-generic-tplink_archer-c7-v2-squashfs-factory.bin (also with a custom build of the HEAD of the openwrt-19.07 branch) I find that "tcpdump -i wlan1 | grep Beacon" shows a lot of packets but "tcpdump -i wlan1 'type mgt subtype beacon'" doesn't show anything (a packet from time to time, but very rarely and way less than without the filter). Doing the same after patching libpcap to force it to do the filtering in user-space fixes the issue.

@openwrt-bot
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RedDwarf:

Actually the same problem also happens with the latest snapshot (https://downloads.openwrt.org/snapshots/targets/ath79/generic/openwrt-ath79-generic-tplink_archer-c7-v2-squashfs-factory.bin).

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RedDwarf:

I have not seen any other bug report, but in the forum there is https://forum.openwrt.org/t/unable-to-filter-for-beacon-frames-with-tcpdump-bug/47841/5, which says the problem happens with both "Archer C7 v2 (QCA9558) and Asus RT-AC51U(MT7620)".

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RedDwarf:

The problem disappears in master (f57230c) doing this

echo 0 > /proc/sys/net/core/bpf_jit_enable

@aparcar aparcar added release/19.07 pull request/issue targeted (also) for OpenWrt 19.07 release kernel pull request/issue with Linux kernel related changes labels Feb 22, 2022
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Labels
flyspray kernel pull request/issue with Linux kernel related changes release/19.07 pull request/issue targeted (also) for OpenWrt 19.07 release
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