From 9c3de619e13ee6693ec5ac74f50b7aa89056a70e Mon Sep 17 00:00:00 2001 From: Toke Høiland-Jørgensen Date: Sat, 12 Feb 2022 00:48:19 +0100 Subject: libbpf: Use dynamically allocated buffer when receiving netlink messages MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When receiving netlink messages, libbpf was using a statically allocated stack buffer of 4k bytes. This happened to work fine on systems with a 4k page size, but on systems with larger page sizes it can lead to truncated messages. The user-visible impact of this was that libbpf would insist no XDP program was attached to some interfaces because that bit of the netlink message got chopped off. Fix this by switching to a dynamically allocated buffer; we borrow the approach from iproute2 of using recvmsg() with MSG_PEEK|MSG_TRUNC to get the actual size of the pending message before receiving it, adjusting the buffer as necessary. While we're at it, also add retries on interrupted system calls around the recvmsg() call. v2: - Move peek logic to libbpf_netlink_recv(), don't double free on ENOMEM. Fixes: 8bbb77b7c7a2 ("libbpf: Add various netlink helpers") Reported-by: Zhiqian Guan Signed-off-by: Toke Høiland-Jørgensen Signed-off-by: Andrii Nakryiko Acked-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/bpf/20220211234819.612288-1-toke@redhat.com --- tools/lib/bpf/netlink.c | 55 +++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 51 insertions(+), 4 deletions(-) (limited to 'tools/lib') diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c index c39c37f99d5c..a598061f6fea 100644 --- a/tools/lib/bpf/netlink.c +++ b/tools/lib/bpf/netlink.c @@ -87,29 +87,75 @@ enum { NL_DONE, }; +static int netlink_recvmsg(int sock, struct msghdr *mhdr, int flags) +{ + int len; + + do { + len = recvmsg(sock, mhdr, flags); + } while (len < 0 && (errno == EINTR || errno == EAGAIN)); + + if (len < 0) + return -errno; + return len; +} + +static int alloc_iov(struct iovec *iov, int len) +{ + void *nbuf; + + nbuf = realloc(iov->iov_base, len); + if (!nbuf) + return -ENOMEM; + + iov->iov_base = nbuf; + iov->iov_len = len; + return 0; +} + static int libbpf_netlink_recv(int sock, __u32 nl_pid, int seq, __dump_nlmsg_t _fn, libbpf_dump_nlmsg_t fn, void *cookie) { + struct iovec iov = {}; + struct msghdr mhdr = { + .msg_iov = &iov, + .msg_iovlen = 1, + }; bool multipart = true; struct nlmsgerr *err; struct nlmsghdr *nh; - char buf[4096]; int len, ret; + ret = alloc_iov(&iov, 4096); + if (ret) + goto done; + while (multipart) { start: multipart = false; - len = recv(sock, buf, sizeof(buf), 0); + len = netlink_recvmsg(sock, &mhdr, MSG_PEEK | MSG_TRUNC); + if (len < 0) { + ret = len; + goto done; + } + + if (len > iov.iov_len) { + ret = alloc_iov(&iov, len); + if (ret) + goto done; + } + + len = netlink_recvmsg(sock, &mhdr, 0); if (len < 0) { - ret = -errno; + ret = len; goto done; } if (len == 0) break; - for (nh = (struct nlmsghdr *)buf; NLMSG_OK(nh, len); + for (nh = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(nh, len); nh = NLMSG_NEXT(nh, len)) { if (nh->nlmsg_pid != nl_pid) { ret = -LIBBPF_ERRNO__WRNGPID; @@ -151,6 +197,7 @@ start: } ret = 0; done: + free(iov.iov_base); return ret; } -- cgit v1.2.3-58-ga151