af_packet: when sending ethernet frames, parse header for skb->protocol

Hi,

I compiled the akpm branch of linux-next and found that my virtual machine didn't get an IP address by dhcp.

git bisect said that the problem is in "af_packet: when sending ethernet frames, parse header for skb->protocol"

https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=0f75b09c798ed00c30d7d5551b896be883bc2aeb

I have double checked, the VM gets an IP address w/o this patch and it does not get an address with this patch.

Let me know if you need any information to investigate this issue.

Thanks.

[avagin@localhost linux-2.6]$ git bisect log
# bad: [4a806113d2dfac9e936089859fdd073b5ff31d2e] debug
# good: [c095ba7224d8edc71dcef0d655911399a8bd4a3f] Linux 3.11-rc4
git bisect start 'akpm' 'HEAD'
# bad: [54578244e06fd945bdab70c3d37b6c311b2b1bc2] Merge remote-tracking branch 'spi/for-next'
git bisect bad 54578244e06fd945bdab70c3d37b6c311b2b1bc2
# bad: [79581039eba18f63be7bc1ea2c43da030708b9a0] Merge remote-tracking branch 'wireless-next/master' git bisect bad 79581039eba18f63be7bc1ea2c43da030708b9a0
# good: [37101b9e3432536727f699e916b3b430cd8ce9e4] Merge remote-tracking branch 'libata/for-next'
git bisect good 37101b9e3432536727f699e916b3b430cd8ce9e4
# bad: [0d0cffdcc6fc4f57080b9a443401e8dad5ca77f8] gianfar: Cleanup TxFCB insertion on xmit
git bisect bad 0d0cffdcc6fc4f57080b9a443401e8dad5ca77f8
# good: [66cae9ed6bc46b8cc57a9693f99f69926f3cc7ef] rtnl: export physical port id via RT netlink
git bisect good 66cae9ed6bc46b8cc57a9693f99f69926f3cc7ef
# good: [9ab5ec59c8a9cc0e4b94252b48200b6023c716aa] tile: support PTP using the tilegx mPIPE (IEEE 1588) git bisect good 9ab5ec59c8a9cc0e4b94252b48200b6023c716aa
# bad: [c483e02614551e44ced3fe6eedda8e36d3277ccc] af_packet: simplify VLAN frame check in packet_snd git bisect bad c483e02614551e44ced3fe6eedda8e36d3277ccc
# good: [b9c119844c42a46a6c6006d158ee33af81fe76ae] qlcnic: Enhance diagnostic loopback error codes. git bisect good b9c119844c42a46a6c6006d158ee33af81fe76ae
# good: [e216975ad97cfcfc436789aa66d59a0e93f337f7] uapi: Convert some uses of 6 to ETH_ALEN
git bisect good e216975ad97cfcfc436789aa66d59a0e93f337f7
# good: [ba5082c71476891623757956ebfc36040ac317e2] Merge branch 'eth_alen'
git bisect good ba5082c71476891623757956ebfc36040ac317e2
# bad: [0f75b09c798ed00c30d7d5551b896be883bc2aeb] af_packet: when sending ethernet frames, parse header for skb->protocol git bisect bad 0f75b09c798ed00c30d7d5551b896be883bc2aeb
# good: [d27fc78208b53ccdfd6a57d4ac44a459ca66806f] sctp: Don't lookup dst if transport dst is still valid git bisect good d27fc78208b53ccdfd6a57d4ac44a459ca66806f

# first bad commit: [0f75b09c798ed00c30d7d5551b896be883bc2aeb] af_packet: when sending ethernet frames, parse header for skb->protocol

Hi,

Thanks for your investigation. I could reproduce your problem, the culprit was the skb->data pointer changed as a side effect in eth_type_trans().

Best wishes, Phil