[PATCH 4.9 46/70] RDMA/rxe: Fix the parent sysfs read when the interface has 15 chars

[Greg Kroah-Hartman]

From: Yi Zhang <yi.zhang@xxxxxxxxxx>

[ Upstream commit 60b1af64eb35074a4f2d41cc1e503a7671e68963 ]

'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>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/infiniband/sw/rxe/rxe_verbs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.c b/drivers/infiniband/sw/rxe/rxe_verbs.c
index 26d66431f95b7..3b24ce8e3b3cb 100644
--- a/drivers/infiniband/sw/rxe/rxe_verbs.c
+++ b/drivers/infiniband/sw/rxe/rxe_verbs.c
@@ -1195,7 +1195,7 @@ static ssize_t rxe_show_parent(struct device *device,
 	struct rxe_dev *rxe = container_of(device, struct rxe_dev,
 					   ib_dev.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(parent, S_IRUGO, rxe_show_parent, NULL);
-- 
2.25.1