[Devel] [PATCH RHEL7 COMMIT] netlink: add an option to set sk->err from userspace

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1127.18.2.vz7.163.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.18.2.vz7.163.41
------>
commit 6bdca3581e557b7370e35e1d471b236afde05e4d
Author: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
Date:   Thu Oct 29 17:00:59 2020 +0300

    netlink: add an option to set sk->err from userspace
    
    Sometimes during dump criu can encounter sockets with overflown kernel buffer,
    which results in ENOBUFS error during next read. We need an reliable way
    to restore sk->sk_err.
    
    v2: add an option to return EINVAL
    
    https://jira.sw.ru/browse/PSBM-120976
    Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
---
 include/uapi/linux/netlink.h |  1 +
 net/netlink/af_netlink.c     | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index 3756be5..62f8b4b 100644
--- a/include/uapi/linux/netlink.h
+++ b/include/uapi/linux/netlink.h
@@ -115,6 +115,7 @@ struct nlmsgerr {
 #define NETLINK_CAP_ACK		10
 
 #define NETLINK_REPAIR2		127
+#define NETLINK_SETERR		128
 
 struct nl_pktinfo {
 	__u32	group;
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 6c99bca..6e0af810 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1542,6 +1542,16 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
 			nlk->flags &= ~NETLINK_F_REPAIR;
 		err = 0;
 		break;
+	case NETLINK_SETERR:
+		err = -ENOPROTOOPT;
+		if (nlk->flags & NETLINK_F_REPAIR) {
+			if (!val || val > MAX_ERRNO)
+				return -EINVAL;
+			sk->sk_err = val;
+			sk->sk_error_report(sk);
+			err = 0;
+		}
+		break;
 	case NETLINK_PKTINFO:
 		if (val)
 			nlk->flags |= NETLINK_F_RECV_PKTINFO;