This is a note to let you know that I've just added the patch titled
libbpf: Use dynamically allocated buffer when receiving netlink messages
to the 5.17-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
libbpf-use-dynamically-allocated-buffer-when-receivi.patch
and it can be found in the queue-5.17 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit a73b63e26c31a3ac06b350509ca25eb840e27c16
Author: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Date: Sat Feb 12 00:48:19 2022 +0100
libbpf: Use dynamically allocated buffer when receiving netlink messages
[ Upstream commit 9c3de619e13ee6693ec5ac74f50b7aa89056a70e ]
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 <zhguan@xxxxxxxxxx>
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Link: https://lore.kernel.org/bpf/20220211234819.612288-1-toke@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 39f25e09b51e..69b353d55dbf 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 @@ static int libbpf_netlink_recv(int sock, __u32 nl_pid, int seq,
}
ret = 0;
done:
+ free(iov.iov_base);
return ret;
}
