[PATCH] nvme: Enter string size calculation “subsysnqn”

[Denis Arefev <arefev@swemel.ru>]

When memory is allocated, the size of the string 
is calculated nvmet_subsys_alloc(...).
When memory was accessed, constant size was used.

Fixes: 95409e277d83 ("nvmet: implement unique discovery NQN")
Reported-by: syzbot+a84181c81389771eb46a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a84181c81389771eb46a
Signed-off-by: Denis Arefev <arefev@swemel.ru>
---
 drivers/nvme/target/configfs.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index eeee9e9b854c..2f74204d000e 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -2247,14 +2247,15 @@ static struct config_group nvmet_hosts_group;
 static ssize_t nvmet_root_discovery_nqn_show(struct config_item *item,
 					     char *page)
 {
-	return snprintf(page, PAGE_SIZE, "%s\n", nvmet_disc_subsys->subsysnqn);
+	return snprintf(page, strnlen(nvmet_disc_subsys->subsysnqn, PAGE_SIZE),
+			"%s\n", nvmet_disc_subsys->subsysnqn);
 }
 
 static ssize_t nvmet_root_discovery_nqn_store(struct config_item *item,
 		const char *page, size_t count)
 {
 	struct list_head *entry;
-	size_t len;
+	size_t len, nqn_len;
 
 	len = strcspn(page, "\n");
 	if (!len || len > NVMF_NQN_FIELD_LEN - 1)
@@ -2271,8 +2272,9 @@ static ssize_t nvmet_root_discovery_nqn_store(struct config_item *item,
 			return -EINVAL;
 		}
 	}
-	memset(nvmet_disc_subsys->subsysnqn, 0, NVMF_NQN_FIELD_LEN);
-	memcpy(nvmet_disc_subsys->subsysnqn, page, len);
+	nqn_len = strnlen(nvmet_disc_subsys->subsysnqn, NVMF_NQN_SIZE);
+	memset(nvmet_disc_subsys->subsysnqn, 0, nqn_len);
+	memcpy(nvmet_disc_subsys->subsysnqn, page, nqn_len);
 	up_write(&nvmet_config_sem);
 
 	return len;
-- 
2.43.0