[PATCH v4] tty: vt: keyboard: add default switch-case, to handle smatch-warnings in method vt_do_kdgkb_ioctl

[Ajay Garg]

smatch-kchecker gives the following warnings when run on keyboard.c :

vt_do_kdgkb_ioctl() error: uninitialized symbol 'kbs'.
vt_do_kdgkb_ioctl() error: uninitialized symbol 'ret'.

This usually happens when switch has no default case and static 
analyzers and even sometimes compilers can’t prove that all possible 
values are covered.


Thus, the default switch-case has been added, which sets the values 
for the two variables :

        * kbs as NULL, which also nicely fits in with kfree.

        * ret as -ENOIOCTLCMD (on same lines if there is no cmd
                               match in "vt_do_kdskled" method).


Many thanks to the following for review of previous versions :

	* Pavel Skripkin <paskripkin@xxxxxxxxx> 
	* Andy Shevchenko <andy.shevchenko@xxxxxxxxx> 


Signed-off-by: Ajay Garg <ajaygargnsit@xxxxxxxxx>
---


There were discussions previously, and the current patch is the 
result.

v1 :
https://lore.kernel.org/linux-serial/YYZN30qfaKMskVwE@xxxxxxxxx/T/#t

v2 :
https://lore.kernel.org/linux-serial/CAHP4M8Vdj4Eb8q773BeHvsW9n6t=3n1WznuXAR4fZCNi1J6rOg@xxxxxxxxxxxxxx/T/#m18f45676feaba6b1f01ddd5fe607997b190ef4b9

v3 :
https://lore.kernel.org/linux-serial/20211106220315.392842-1-ajaygargnsit@xxxxxxxxx/T/#u

Changes in v2 :

        * Changes as required by scripts/checkpatch.pl

        * Checking whether kbs is not NULL before kfree is not required,
          as kfree(NULL) is safe. So, dropped the check.

Changes in v3 :

        * Using default-switch case, and setting the variables 
          when there is no matching cmd.

Changes in v4 :

        * Removed braces for the default switch-case.


 drivers/tty/vt/keyboard.c | 6 ++++++
 1 file changed, 6 insertions(+)


diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index c7fbbcdcc346..f66c32fe7ef1 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -2090,6 +2090,10 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
 
 		ret = 0;
 		break;
+	default:
+		kbs = NULL;
+		ret = -ENOIOCTLCMD;
+		break;
 	}
 
 	kfree(kbs);

-- 
2.30.2