target: Allow non-supporting backends to set pi_prot_type to 0

Userspace tools assume if a value is read from configfs, it is valid
and will not cause an error if the same value is written back. The only
valid value for pi_prot_type for backends not supporting DIF is 0, so allow
this particular value to be set without returning an error.

Reported-by: Krzysztof Chojnowski <frirajder@gmail.com>
Signed-off-by: Andy Grover <agrover@redhat.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Cc: stable@vger.kernel.org # 3.14+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index 65001e133670..382b66b212ae 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -936,6 +936,10 @@ int se_dev_set_pi_prot_type(struct se_device *dev, int flag)
                 return 0;
         }
         if (!dev->transport->init_prot || !dev->transport->free_prot) {
+                /* 0 is only allowed value for non-supporting backends */
+                if (flag == 0)
+                        return 0;
+
                 pr_err("DIF protection not supported by backend: %s\n",
                        dev->transport->name);
                 return -ENOSYS;