FAILED: patch "[PATCH] RDMA/rxe: Fix the parent sysfs read when the interface has 15" failed to apply to 4.9-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 60b1af64eb35074a4f2d41cc1e503a7671e68963 Mon Sep 17 00:00:00 2001
From: Yi Zhang <yi.zhang@xxxxxxxxxx>
Date: Thu, 20 Aug 2020 23:36:46 +0800
Subject: [PATCH] RDMA/rxe: Fix the parent sysfs read when the interface has 15
 chars

'parent' sysfs reads will yield '\0' bytes when the interface name has 15
chars, and there will no "\n" output.

To reproduce, create one interface with 15 chars:

 [root@test ~]# ip a s enp0s29u1u7u3c2
 2: enp0s29u1u7u3c2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN group default qlen 1000
     link/ether 02:21:28:57:47:17 brd ff:ff:ff:ff:ff:ff
     inet6 fe80::ac41:338f:5bcd:c222/64 scope link noprefixroute
        valid_lft forever preferred_lft forever
 [root@test ~]# modprobe rdma_rxe
 [root@test ~]# echo enp0s29u1u7u3c2 > /sys/module/rdma_rxe/parameters/add
 [root@test ~]# cat /sys/class/infiniband/rxe0/parent
 enp0s29u1u7u3c2[root@test ~]#
 [root@test ~]# f="/sys/class/infiniband/rxe0/parent"
 [root@test ~]# echo "$(<"$f")"
 -bash: warning: command substitution: ignored null byte in input
 enp0s29u1u7u3c2

Use scnprintf and PAGE_SIZE to fill the sysfs output buffer.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 8700e3e7c485 ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20200820153646.31316-1-yi.zhang@xxxxxxxxxx
Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Yi Zhang <yi.zhang@xxxxxxxxxx>
Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.c b/drivers/infiniband/sw/rxe/rxe_verbs.c
index bb61e534e468..756980f79951 100644
--- a/drivers/infiniband/sw/rxe/rxe_verbs.c
+++ b/drivers/infiniband/sw/rxe/rxe_verbs.c
@@ -1056,7 +1056,7 @@ static ssize_t parent_show(struct device *device,
 	struct rxe_dev *rxe =
 		rdma_device_to_drv_device(device, struct rxe_dev, ib_dev);
 
-	return snprintf(buf, 16, "%s\n", rxe_parent_name(rxe, 1));
+	return scnprintf(buf, PAGE_SIZE, "%s\n", rxe_parent_name(rxe, 1));
 }
 
 static DEVICE_ATTR_RO(parent);