From b29799d2537ee59710a57c5e8b123eb4986e3d08 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Tue, 11 Sep 2018 14:09:11 -0700 Subject: [PATCH] tools/bpf: fix a netlink recv issue MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Commit 7db325d1d0a2 ("tools/bpf: move bpf/lib netlink related functions into a new file") introduced a while loop for the netlink recv path. This while loop is needed since the buffer in recv syscall may not be enough to hold all the information and in such cases multiple recv calls are needed. There is a bug introduced by the above commit as the while loop may block on recv syscall if there is no more messages are expected. The netlink message header flag NLM_F_MULTI is used to indicate that more messages are expected and this patch fixed the bug by doing further recv syscall only if multipart message is expected. The patch added another fix regarding to message length of 0. When netlink recv returns message length of 0, there will be no more messages for returning data so the while loop can end. Fixes: 7db325d1d0a2 ("tools/bpf: move bpf/lib netlink related functions into a new file") Reported-by: Björn Töpel Tested-by: Björn Töpel Signed-off-by: Yonghong Song Signed-off-by: Alexei Starovoitov --- tools/lib/bpf/netlink.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c index 469e068dd0c5f..fde1d7bf8199e 100644 --- a/tools/lib/bpf/netlink.c +++ b/tools/lib/bpf/netlink.c @@ -65,18 +65,23 @@ static int bpf_netlink_recv(int sock, __u32 nl_pid, int seq, __dump_nlmsg_t _fn, dump_nlmsg_t fn, void *cookie) { + bool multipart = true; struct nlmsgerr *err; struct nlmsghdr *nh; char buf[4096]; int len, ret; - while (1) { + while (multipart) { + multipart = false; len = recv(sock, buf, sizeof(buf), 0); if (len < 0) { ret = -errno; goto done; } + if (len == 0) + break; + for (nh = (struct nlmsghdr *)buf; NLMSG_OK(nh, len); nh = NLMSG_NEXT(nh, len)) { if (nh->nlmsg_pid != nl_pid) { @@ -87,6 +92,8 @@ static int bpf_netlink_recv(int sock, __u32 nl_pid, int seq, ret = -LIBBPF_ERRNO__INVSEQ; goto done; } + if (nh->nlmsg_flags & NLM_F_MULTI) + multipart = true; switch (nh->nlmsg_type) { case NLMSG_ERROR: err = (struct nlmsgerr *)NLMSG_DATA(nh); -- 2.39.5