On Fri, Mar 27, 2020 at 5:11 AM David Ahern dsahern@gmail.com wrote:
On 3/26/20 2:28 PM, Johannes Berg wrote:
And looking at this ... well, that code is completely wrong?
E.g.
rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET, cmd_type, &tid, sizeof(__u32));(cmd_type is one of TASKSTATS_CMD_ATTR_TGID, TASKSTATS_CMD_ATTR_PID)
or it might do
rc = send_cmd(nl_sd, id, mypid, CGROUPSTATS_CMD_GET, CGROUPSTATS_CMD_ATTR_FD, &cfd, sizeof(__u32));so clearly it wants to produce a u32 attribute.
But then
static int send_cmd(int sd, __u16 nlmsg_type, __u32 nlmsg_pid, __u8 genl_cmd, __u16 nla_type, void *nla_data, int nla_len) { ...
na = (struct nlattr *) GENLMSG_DATA(&msg);// this is still fine
na->nla_type = nla_type;// this is also fine
na->nla_len = nla_len + 1 + NLA_HDRLEN;// but this??? the nla_len of a netlink attribute should just be // the len ... what's NLA_HDRLEN doing here? this isn't nested // here we end up just reserving 1+NLA_HDRLEN too much space
memcpy(NLA_DATA(na), nla_data, nla_len);// but then it anyway only fills the first nla_len bytes, which // is just like a regular attribute.
msg.n.nlmsg_len += NLMSG_ALIGN(na->nla_len);// note that this is also wrong - it should be // += NLA_ALIGN(NLA_HDRLEN + nla_len)
So really I think what happened here is precisely what we wanted - David's kernel patch caught the broken userspace tool.
agreed. The tool needs to be fixed, not the kernel policy.
I do not get the error message with this change as Johannes points out above:
diff --git a/tools/accounting/getdelays.c b/tools/accounting/getdelays.c index 8cb504d30384..e90fd133df0e 100644 --- a/tools/accounting/getdelays.c +++ b/tools/accounting/getdelays.c @@ -136,7 +136,7 @@ static int send_cmd(int sd, __u16 nlmsg_type, __u32 nlmsg_pid, msg.g.version = 0x1; na = (struct nlattr *) GENLMSG_DATA(&msg); na->nla_type = nla_type;
na->nla_len = nla_len + 1 + NLA_HDRLEN;
na->nla_len = nla_len + NLA_HDRLEN; memcpy(NLA_DATA(na), nla_data, nla_len); msg.n.nlmsg_len += NLMSG_ALIGN(na->nla_len);
Right. This is the right thing to do. I missed that the nla_len() will minus the NLA_HDRLEN.
Would you pls. submit a patch ?
Feel free to add: Tested-by: Yafang Shao laoar.shao@gmail.com
Thanks Yafang