[Swan-dev] coverity warning in nic offload : shifting by negative amount has undefined behavior

[Antony Antony]

Hi Ilan,

There is a coverity warning in the recently added nic-offload code. I do not
understand the related code completely to fix it myself.

Would you please take a look? and see if you can fix it.

programs/pluto/kernel_netlink.c:979  netlink_detect_offload

 976
 977        /* Feature is supported by kernel. Query device features */
 978        blocks = (netlink_esp_hw_offload + 31) / 32;
    CID 1452850 (#1 of 1): Bad bit shift operation (BAD_SHIFT)4. 
negative_shift: In expression 1 << netlink_esp_hw_offload % 31, shifting by 
a negative amount has undefined behavior. The shift amount, 
netlink_esp_hw_offload % 31, is -2.
 979        feature_bit = 1 << (netlink_esp_hw_offload % 31);
 980
 981        cmd = alloc_bytes(sizeof(*cmd) + sizeof(cmd->features[0]) * 
blocks, "ethtool_gfeatures");

netlink_esp_hw_offload could be -1. I am not sure about -2?

when netlink_esp_hw_offload == -1i
netlink_esp_hw_offload % 31 =  -1

1 << -1 is undefined.   possiby bad things can happen. It is wort looking 
into.

-antony